When you've finished playing a game, what do you do with it? A lot of stores offer credit towards another game if you trade one in. There are lots of ways to sell today - online, to friends, pawn shops, and others. Or would you rather just keep your games? Also, what about consoles? Do you keep old ones when you get the next generation machines?
I usually keep my games, but I have sold a few I knew I wasn't going to play any more. I keep my consoles too, but I did sell my first NES a year or two ago. It mostly didn't work any more, though.