Price flexibility is the key. There are games I'd be fine paying $40 for (mainline Mario, Zelda, Metroid, and the like), but there's a lot of stuff that would still need to be $30 or $20. Also, remember that there were developers early in the DS's life (I know EA did it, and I think there were others) that tried to charge $40 for DS games, and they quickly went back down to $30 once they realized people weren't willing to pay that.