Am I missing something? Last I saw, Blizzard was not going to make anything on AH transactions... Are you assuming this or was it stated somewhere? http://www.diablowiki.net/Auction_House
I'm not saying this wiki is "bible", but I believe they are correct (you can find this in many different sites with a Google search) -
"This entire subject is rather a moral and ethical, not to mention ‘’legal’’, quagmire. Yet, Blizzard has always opposed these transactions for the reasons listed above, and others. Their reasoning for finally allowing it, in their own game no less, is twofold: they are able to control the transaction, and they are also able to profit from it.
A player will no longer feel the need to go to unreputable websites which may contain malicious software that steals their personal or account information. All of these transactions now take place within the game’s client."