I think you are right in a sense, but some of the great grandmasters of chess were also some of the smartest men alive. Studying and effort will get you better, in my opinion.
Peak rating? I doubt it

I think in this way, Chess is no different from any other intellectual activity. There probably isn't a defined limit or "roof" for each of us beyond time. That's everyone's limit. I believe the only difference between us mortals and players like bobby fisher or Capablanca is the time it would take us to get there. Sometimes a lifetime can prove not enough for a slower improvement rate.
Probably there's no theorical "peak rating" but there is a practical one that comes from the avaiable time we get to study chess and the natural potential each of us have for it.

I think there is a matter of some inherent talent involved, not only in chess but in other endeavors such as guitar playing for example. Most people could study and practice for a hundred years and still not be able to play like Andre Segovia or Jerry Garcia or Eric Clapton. Most Grandmasters were prodigies, not just Bobby Fischer and Capablanca.

OK sure, but I don't think chess is in that realm (or languages which is the other tried argument). Becoming a 'Jerry Garcia' requires some great conflux of talent and opportunity, chess is not the same. Brilliance is less artistic than it is mathematical. Which leads to the obvious claim that there is no such thing as a limit (anymore than there is with math, which doesn't exist). Take Lasker for example who had precision beyond us mere mortals. If I'm wrong so be it, but I think anyone can become grandmaster over time (see the polski (sp?) sisters in Wikipedia. "geniuses are created not born")

I have to admit that Fischer seems like he wasn't born for this world. That is the only just way to describe him. And while I don't know enough about Karpov (I know you cited Kasparov), I feel confident saying that Kasparov just wanted it bad enough. I think anyone would be hard pressed to find another player who put so much into the game for as long as Kasparov has. All of the best devoted every non-pecuniary hour to the game. I don't, and I won't, but that, in my opinion, is the difference.
If I am wrong in my assessment of the best, let me know. I feel pretty confident that from Alekhine down (no claiming Morphy!) every 'great' made sacrifices we would call crazy.
If we all devoted our time to chess, we may not individually be the next great, but I believe the Polgar family knows (according to wikipedia :)!) that geniuses are made, not born.

Oh, just missed a very important point: TONYDAL said: Nowadays most professional players peak somewhere around 30.
is this true? I guess that if it is there is a 'peak' then, sadly for me and many other amateurs

Agree 100%! Anyone & Everyone should be able to reach a grandmasters ranking given they spend the time & put the effort to make it!!!

Im not so sure. I think that some people have more natural ability than others, just as this is true for athletics.
There are other factors however, and often they work against each other. Time is the issue for most people. We don't have enough time to train to a master level, not in terms of hours per day or hours per lifetime.There's also the issue of age and how as we spend more and more of our lives looking to become great, our age slowly destroys our peak ability.
Basically what im trying to say is that for the normal person, it would be impossible to train enough to become a GM before its too late and your getting too old.

The thing about a rating plateau is that nobody knows when they've hit it. If you think you've hit your plataeu, it probably means one of a few different things:
#1 Your learning methods are ineffective
#2 Your dogmas only let you get so far
#3 You had difficulty increasing in rating so you decided 'im at my plataeu' and then it became a self-fulfilling prophecy because you believed it.
If anything I think this is really important to realize because so many people I've encountered seem to feel this way. For instance, a person could be normal for years but then have a couple problems, and once he gets a 'diagnosis' he feels like suddenly he has no control over himself anymore because his doctor said 'add' or 'depression' or whatever.
At that point, if you give them solutions, they say something like: "I can't, I have depression" Or "I can't, I have add", without even trying.
What's even sadder is when a child ata very young age defines themselves as 'stupid' or something because of early failures, and never tries again.
In fact, I used to feel very very guilty when I was starting to accomplish something big in my development in any of the games or skills I do. I also felt afraid - I felt like I was approaching a level of actual good skill, but that eventually I would not succeed completely and fail miserably, and find out that I had a limit.
In my opinion though, the only factor about how good you will get is how much intensity you put into the game. Not training time, not number of games, etc. I went on binges playing thousands of games with 0 improvement. Other times I played less than 1 game a week and yet improved in my own mind during the entire weak, either subconsciously or by examining concepts. When I started watching the Josh Waitzkin lectures in chessmaster with a view to understanding them instead of just rejecting them instantly in my mind "Maintaining the tension? What is this psychological nonsense? Teach me chess truth, Josh!" I leaped in strength from strong 1800 player to roughly 2000 player in a very short amount of time.
There's a lot of zen stories and other stories about this kind of thing. I mean seriously - are you putting your ultimate effort into your chess training? Are you asking yourself the questions you need to ask to understand chess, instead of being lazy and 'worrying about it later'? If you have an hour to play, are the games intense or are you just shuffling pieces around?
If you put the right 1400 level player in the right frame of mind in the right situation, they will play like a 1900 player. I'm not joking. So much of this game, as well as many other games, is determined by things like confidence and mood.
So many players lose their games to higher rated opponents before they even begin.

When tonydal said 30 is a peak... I think he meant for GM's... obviously if you haven't learned chess until 50 you are going to get better as you play/learn/study ect. But 30 is the peak age for probably elite grandmasters who started decades ago, or something close maybe.

I would say that chess takes both crystallized intellect (stuff you've learned) and fluid intellect (thinking on your feet). As you get older you have more crystalized and less fluid. I'm guessing that you play your best chess at a certain balance between the 2.

that's interesting, and I can't really argue with you seeing as how I'm under 25, and I admit that I will never become a grandmaster (although I'm not sure it is necessarily because of ability, it may just be because I only got serious about chess 2 or 3 years ago whereas most GMs train since childhood). While Fischer was better at 15 than I could hope to be in 7 or 10 years, I think that learning does slow the older you get (although it still exists) so his early 10 years will be far more productive than mine.
All that I want to stress is that this idea of a peak or ceiling I think is artificially imposed to explain away a lack of improvement (not saying that's the case with any one in particular though, as I can't speak for people on this site). Perhaps I'm just too young to be anything but optimistic.

that's interesting, and I can't really argue with you seeing as how I'm under 25, and I admit that I will never become a grandmaster (although I'm not sure it is necessarily because of ability, it may just be because I only got serious about chess 2 or 3 years ago whereas most GMs train since childhood). While Fischer was better at 15 than I could hope to be in 7 or 10 years, I think that learning does slow the older you get (although it still exists) so his early 10 years will be far more productive than mine.
All that I want to stress is that this idea of a peak or ceiling I think is artificially imposed to explain away a lack of improvement (not saying that's the case with any one in particular though, as I can't speak for people on this site). Perhaps I'm just too young to be anything but optimistic.
It's like learning a language. If you learned English at age 20, no matter how hard you try, you'll always have an accent.

Agree 100%! Anyone & Everyone should be able to reach a grandmasters ranking given they spend the time & put the effort to make it!!!
I totally disagree with what you wrote...
answer me why only 2% of society has IQ above 150 ? you really think that everybody can be a GM. World is not fair my friend ;)
There are estimations that gives you your maximal elo like:
Max Elo = (10*IQ) +1000
So if you take an avarage man with IQ=120 then he can if he spent enough time on it reach the level of CM (2200)
That would explain why so many people say that they develop constantly, becouse they learn chess to short and are not at their peak

I hit several peaks in the past week, and I will fall from every one. Still, there are higher peaks ahead. Eventually, age will catch up with me as I gain experience, and the highest peaks will be behind me.
I've been playing long enough to know that I don't have the innate talent to get to GM or IM, nor probably FM or NM. I might yet make expert before age 60 if I succeed in getting to USCF Class A before 50. I am so close. My achievements in chess all come from hard work. Had I started working harder thirty years ago (when I all but gave up chess for most of fifteen years), master would be in my grasp today, or at least within reach.
I am over 2400 on one turn-based site, although I have not played there for several years and I'm better now. But ratings are relative to pools. The 1800s there play like 1400s here.
I've heard this rumor for years, that eventually everyone hits their 'peak rating.' Frankly, I don't buy it. I could understand if the argument were that at some point you get too old to play well (like over 80). But people talk about it as if everyone were born with some finite potential, and I fail to understand how chess puzzles, playing new/old lines fails to give someone improvement. From my own personal experience, I find that I don't grasp all the concepts that people who are better than me do, but I also find that as I keep playing and studying, I begin to understand concepts that once were lost on me. In this way I always have something new I am learning, and I can't understand why it should ever stop.
Chess is very heavily weighted towards experience and effort, so unless one stops putting in the effort, I can't imagine why they can't get better. Albeit Master is not even within view of my telescope (yet), I'm pretty sure the stronger players studied more for longer and thats HOW they got good. Am I totally off base or does this seem to make a lot of sense?