Dead wrong
People only play these things for as long as they have fun doing it. I routinely cease forever playing a game because I've figured out all that I want to about the game and it's not fun any more.
If a designer can keep me playing something for 200hrs, then that game is 100hrs better that the game I quit after 100 hrs. If they can keep me playing for 300hrs then God bless 'em those designers are geniuses. And man did I get my money's worth!