I suppose it doesn't really matter to a rabid internet community that smells betrayal or a lack of caring on the development team's part where there is none, but the thing with any development cycle, let alone a 9 year long one, is that it's a process of change.
They didn't decide 9 years ago how this game would end up. The gaming community changes across that period of time, and so do game design sensibilities. Take that into account, and then know that a process like game development is one that only the development team is privy to on a day-to-day basis, and you see how games evolve to be something placed in the current situation.
This sadly happens to a great many games, where everyone can sit back at the end of development and internet armchair criticize design decisions to hell and back and ask "how did they not see this?". Truth is though, that hindsight is 20/20, and when you're in development you simply try to make the best game you can, regardless of what it ends up being relative to whatever game came before it.
I still think Diablo 3 is a pretty great game. It's got some problems, and I know Blizzard are continually assessing and adjusting the game's balance to counter the problems they can tackle. The auction house playing the role it does is an unfortunate thing but I don't believe it's reasonable to start doubting the development team there for the way that has played out. As far as I'm concerned, they can still pull the auction house and the RMAH back on the rails, but they need to contain their economy a bit.