Some people do plateau but the reason they don't get better is because they give up, so to speak.
I both agree and disagree with zircon. People who put a colossal amount of time in are going to figure precision details that give them significant edge. Sometimes though, someone just has better finger coordination than the other 15 guys. Incidentally, it's those people who are going to put a vast amount of time into the game because they have an original skill.
So, thinking it through I guess in a general way zircon is right.