You'd think the publishers would understand this and see that it really is a circular process. I'm pretty sure EA would have no problem with me trading in Turd Fighter 3 and Same Old RPG for credit towards NBA 09. Or even 2 of their other sports titles, for a new one. Everyone wins, but they just don't see it that way.
I have no problem with Gamestop. If you have a problem with their over-priced used games, then go somewhere else. I don't normally buy a 1 month old game for $5 less than new, but I'll be more than happy to pay $8 for a used title, over a new one at $19.99.

