Well the first thing that pops into my mind is that they're re-packing games. I mean it's pretty odd to have say 60 pre-owned games AND to have 50 of them available as brand new.
Mind you, they do the same with consoles too, and that's just bizarre.
*edit* although, if you're chanrging $1000 for a console you could probably actually forge a box and still make a killing.