We still think that's true for a MMO in which thousands of players co-mingle in a persistent world and vie for supremacy in eSport competitions or 'world first' boss kills in raids. Neither of these are true though for a co-op action RPG.
The worst that could happen is you open your game up to the public, someone jumps in wearing some awesome gear, and you don't know if he found those items himself. But that'd be the case whether we offered an official way to buy items from other players or not.
The same is not true for Diablo in which all items are randomized in both affixes and drop chances from all enemies. We know that trading is necessary in Diablo games to build a solid character as you could play forever and still never see a specific item you're after.
This has to be one of the most idiotic responses I've read from a Blizzard representative.
1 )Thousands of players don't compete for world first boss kills in raids (and even if this were the case, thousands is a small % of the 11.5 Million subscribers WoW has)
2 )You can't buy the best PvE or PvP gear from 3rd parties.
3) Buying gold doesn't give you huge advantage over other players because the gear you can buy with it is not high end.
4) What "e-sport" are we talking about here? The Arena Tournament? Aren't players given everything (characters, gear) and all they need to put is their skills? What role do gold sellers play here? If you are talking about the normal ladder, what difference will buying gold make if gold can't buy skills?
Bottom line here is. Blizzard wants to make "EXTRA" money out of Diablo 3 to compensate for the lack of a subscription. Why the hell would anyone in their right mind use the gold AH when there is a real money alternative? You assume that your player base is an educated one, but after 7 years with WoW you still haven't realized that the bulk of those 11.5 Million are kids, idiots or ignorant people who react first, then think after.
Are you going to sell the game for 59.99 to everyone in the planet or make 50% off exceptions to the Chinese (as you do with their WoW subs) and allow them to play in U.S. Gateways so Chinese companies buy millions of copies and flood said servers with Chinese farmers who will undoubtedly flood the AH with 24/7 farmed items? In either case you had that in mind as well right? More money to Blizzard from extra copies and AH fees?
A normal AH is a good idea. It can potentially save you time to get a desired item (instead of spending hours in trade chat or joining "trading games"). However, any player with an IQ above 70 will know that the main reason behind the $$$ AH is greed.