Whether that is a good deal for Blizzard depends on how much the real money auction house ends up being used. I experimented with the gold-only version in the Diablo 3 beta, and personally I am not a big fan. Not that it isn't working, but just the opposite: The auction house works far too well for equipping your character. Far better than the random loot drop system. Thus if you use the auction house, the chance of finding a random drop which is useful for you diminishes dramatically. And that makes the game considerably less fun. I even stopped crafting and sending items between characters through the common bank for that reason. At the heart of it, Diablo has always been a game about collecting loot. Replace that by something more efficient, and you get a less fun game.
So what do you think? Will you be buying items for real money on the Diablo 3 auction house?