All this will do is make users use external auction houses. As long as they keep in-game trading of rare and legendary items, people will just take it to eBay or some other site, and then arrange the swap in-game.
It makes it less instant gratification, but won't stop the buying of items.
Which is fine, IMO. Removing the AH as a crux of gameplay design is the important thing here. Trade isn't inherently bad, but building the entire game around trade (and more specifically, trying to build the game around incentivizing people to trade through your system for real currency of which you get a cut) is a really crappy thing to do to a loot grinder.
Do you have any sources which confirm that Blizzard built the game around AH monetization? I see this claim made frequently, but I've never actually seen anything that wasn't pure speculation.
They've never explicitly said "Yeah, we built to game to try to juice as much out of you through the RMAH" if that's what you're asking. It's pretty clear if you actually played the game, though. The game was tuned, both in terms of difficulty and drops, with the expectation that the player would be using the AH[1], and Blizzard built the RMAH in order to attempt to capitalize upon the sales that previously happened through D2JSP or whatnot.
It's exceptionally clear that Blizzard's idea was to control scarcity of desirable items so that people were incentivized to buy and sell these most desirable items for real money, giving Blizzard their 15% cut on every sale. We have a scenario in which the same entity that brokers sales (for a fee!) is the same entity that (arbitrarily) controls the production of items sold -- it doesn't take an MBA to connect the dots there.
No, I can't prove any of this. I would be exceptionally surprised if anyone could. But companies of Blizzard's scale don't do things like a real-money marketplace (from which they take broker's fees) just because "the community demands it" - that absolutely was the monetization strategy for the game. People don't pay a subscription fee, or purchase microtransaction items in the traditional sense. How else are you going to monetize it?
(They had a similar monetization strategy for Starcraft 2, IIRC. Something about a marketplace for community-created content that, again, they would take a cut of. Let the players do the work, take a cut of it. I don't play SC2, so I'm not sure how this shook out.)
Blizzard monetized the game by selling it for $60 a copy.
That image you linked shows that the drop rates for items take into account the existence of the auction house. That sounds like a purely game balance decision. I.e., it would still be true even if only the gold auction house existed.
I never got all the outrage over the existence of the auction houses. In Diablo 2 you'd grind for hours looking for good drops and then have to spam chat rooms and trade with people. In Diablo 3 you'd do the same grinding but just for gold, and then you buy what you need on the auction house with that gold. What's the difference? (Other than in Diablo 3, once you're done grinding its much easier to get what you want.)
I don't think they really feel the need to completely stop the buying of good items. They just want to decrease their availability so that most players can experience the fun of finding items themselves.
It makes it less instant gratification, but won't stop the buying of items.