@ tye, selling games, and the product protection plans that come with them, is their only source of income. think of them as a pawn shop that's only for games.
the markup is a ripoff, but it's how they stay in business.
gba games are like $5, and i don't mind paying that much for the few kickass ones (castlevania: circle of the moon, golden sun, etc)
but yeah. anything this-gen/easily buyable online is a ripoff, and i wouldn't give them my used games. ever.
oh, and @ jasonburrows.. i think.
steam is an online digital distribution platform, which is a fancy term for online video game store. you download a client, and make an account. at that point, you can buy games, download demos/mods, and manage your game library in the nifty steam client. there's a "community profile" page for you, friends list/chat (including groups and group chats), and lots more neat-o stuff like betas and LOTS of sales on PC games.
worth a shot. alien swarm is free.