Because unhappy customers are likely to spend money on RMAH? That doesnt sound right.
I think they've calculated how many people they need playing to continue to make supporting D3 a profitable venture, and it's probably a lot less than the 6 million copies that they sold early on. And I believe that this necessary fan-boy core of players will continue to play with just some minor patching here and there, especially once PvP comes out. Because that's where the fan-boy core will congregate, and that's where they'll spend their money.
Any real changes to the way the game works, especially with respect to drops and a more interesting and self-sustaining endgame will go against Blizzard's business model twofold: better drops means less dependability on the Auction Houses, and more patch/content support means higher personnel costs, an investment that doesn't really yield any short term financial return.