Because there are a lot of Steam games and I thought it'd be better if they all had the same style, like branded game re-releases. (Sold-Out, Xbox Classics, Xplosiv etc)
And I agree with not having cases for digital distribution, but being as Steam generates backups which can be burned directly to a CD, why pass up the chance to fill your shelves with some shiny photoshop goodness?
I think it's pointless to replace the lovely SNES/N64 cardboard boxes with plastic cases, no matter how knackered they may be. Each to their own, I guess. Anyway, I mainly made this cover to my liking, it wasn't originally going to be released to the public.