I may not be addressing TotalBiscuit's argument very well (I'm not familiar with it)

For a digital good, this is not true - a used copy of a game is identical to a new copy of said game, and offers no incentive to ever buy the new copy instead.

Except for the fact that a new copy must be bought for the used copy to exist. The publisher doesn't release used copies. Used copies exist at the whim of the original owner, and are in much shorter supply. As such, if you really want the game badly and you want it NOW, you'll buy it new. If price is more important that immediacy, you'll wait for it to show up used.