* Penalizing players for dying for longer and longer periods of time
* Penalizing players for playing in groups
I suspect these were simply misguided design decisions aimed at making the game "challenging". Difficulty was entirely out of whack at launch across the entire game (yes, partly because the developers vastly underestimated the effect of the AH), and I suspect this was simply part of it.
* Limiting in-game communication systems severely
I have no way to prove it, but I'm almost certain this was a result of some bizarre political battle inside Blizzard. Battle.net 2.0 came out with Starcraft 2 with the same boneheaded decisions - no chat rooms, the RealID fiasco, etc. - and Diablo 3 simply inherited that mess. There HAVE to be people inside Blizzard who understand why players might find chat rooms valuable, but for some reason they never made themselves heard. I don't think this has much to do with the AH.