Since you can trade WOW (and many other MMOs’) items for real world cash, I wouldn’t call Blizzard bucks useless. In fact I’ve heard people playing WoW for a living...
Basically, say Blizzard compensates you $20k in Blizzard bucks, and you auction off $20k worth of items at a reduced rate, you end up taking $20k * discount rate from Blizzard’s revenue, roughly speaking.
