CHESS CERTAINLY IS KINDA CRAZY
Someone please explain the rating system in online chess?

To get your question answered, you have come to the wrong neighborhood, but you can hope for someone to help out anyway, who points you in the direction of the Help & Support section. And hey, surprise, it is one of the most commonly asked questions: http://support.chess.com/Knowledgebase/Article/View/16/13/how-do-ratings-work
I can tell you why the one guy got 70 points for winning, I did too when I first started here. I'd lose a bunch of points for a loss and get a lot when I won. I think it's trying to find what your rating here should be. Not to sure about the other questions though.

chess.com uses a second number in its calculations called the RD. RD stands for rating deviation. It has to do with how accurate your rating is considered. The lower your RD is, the more accurate your rating is considered to be. The more frequently you play, the lower your RD. If you stop playing altogether, your RD will steadily go back up.
For a simple example of how it affects calculations, let's say you are rated 1200 and you beat a 2000 rated player. If the 2000 player's RD is very low (considered pretty accurate), you will see a very large jump in your rating. If the 2000 player's RD is very high (considered less accurate), you will still see a jump, but it won't be nearly as big.
The calculation also considers your own RD. The lower your RD, the smaller the jumps, the higher, the bigger the jumps.
My highest online rating was 1490. I noticed that during a game with an upper 1500's rated player, I would've lost 10 points if I lost the game. In another game, my opponent was rated 1404, I was rated 1490, and when I lost, his rating raised 70 points!
Seems kinda crazy to me...
Also, I thought that once you started a game, and your opponent had risen in rating since (eg, I started playing a game with a player rated about my rating at the time, and during the course of our game, his rating raised to upper 1600's. After I lost, I still lost 10 points)...I thought the number of rating points you lose would decrease accordingly in such a case, due to your opponents increase in rating, but apparently all that matters is their rating when you start the game.
Anyone?