I'm really surprised how people seem to think diablo 3 wont have an item shop?
What, does all it take is that 'oh, it's players selling to players!'? That's enough to baffle peoples senses?
Let's make it clear - players can only sell to other players because blizzard makes their sale possible.
Blizzard makes a cut on each sale, that it made possible to do.
How is this not an item shop?
Blizzard is being smart with the revenue coming in from this system: players will be charged a flat fee to list an item, and if it sells there will be another flat fee paid to Blizzard. The company won't make more profit on a more expensive item, and the "nominal" fee will dissuade players from simply dumping everything they find on the auction block. Since drops are random and only players can sell to other players, the economy is still self-contained.
What's this self contained bit? It's self contained when it's a blackmarket at well? What's new?
Further, if you can sell stacks of items the "The company won't make more profit on a more expensive item" is completely untrue. A stack of 50 healing potions having the 'same' posting fee as awesome sword X isn't the same. The fee is divided by 50 in one case. Which means awesome sword grants a bigger profit.
I think there are a few stars in peoples eyes, out there. Or perhaps they are snow blind?