Wouldn't amateur be better suited in what you are describing than beginner? An amateur usually knows all of the fundamentals and is attempting to put what knowledge he knows into acquiring a higher understanding of the game, where as a beginner is still struggling with learning the rudiments of the game.
It's weird, but somehow it seems right to me to still call someone who is merely at a low level at chess, regardless of experience, a "beginner", as if they still haven't got past the beginning of chess learning. I'm assuming it's most likely because that's how most people throw around the word beginner when it comes to chess, so I get used to it.
So really this whole thing is pointless, because we all have different precise opinions about when to use the term "beginner", yet I still don't mind discussing it
But as for an actual answer to the original question, I end up agreeing with heinzie. C players at least avoid hanging pieces the vast majority of the time and are starting to learn more advanced concepts; not executing them well, but they're in the process. B players start to execute these ideas reasonably but are still inconsistent, while A players continue to improve in these areas and perhaps get a deeper appreciation for how each part of the game works in harmony with each other, and I say that because at this point they need some motivation for balancing their play: working on the part they're not so good at (like very often the endgame, as in my case) because just one weak link can singlehandedly drag down your game.
Experts I think have a lot of the qualities of masters, like having the ability to intuitively find the move that "the board is screaming for", having strong calculation, always having a plan, lack of unforced errors, etc, just executed in a less consistent way. I think they would still have many more "what was I thinking?" moments, as their decision making process continues to mature, and have more blunders and visible holes in their play, but nevertheless they're getting close to a very respectable level of play, a level that used to seem invincible to me.