I don't think the used market is that big of a problem. I think it's Gamestop + greed. Gamestop pushes the hell out of used games and that makes the used market bigger than it would normally be. Remove Gamestop, and I'll bet more people would buy games new. Developers/publishers have also gotten greedy. Used game sales were never a problem before, so why are they now? What makes games different than books, DVD's, or anything else?
Actually, I'm convinced that efforts to reduce used game sales are a direct result of Gamestop's force-it-down-your-throat used game sales tactics.
BTW, I do think Gamestop is the devil. Not sure if that came across in my post, so I thought I'd add it.