There is a massive difference between an auction house and the current trading chat/forum auctions we have. Auction houses are notorious for ruining entire markets, if not entire games.
Auction houses have to be implemented basically perfectly to not ruin games. Implementing them into a nearly 10years old running economy also can lead to massive issues real quick.
Also, having to interact with the seller/buyer helps the game as well. Especially for a game with such a "small" community, in comparison to other really big MMO games like WoW, it is needed.
There are also some other issues which come along with an auction house, however I will not disclose those here since they shouldn't be a topic at all to begin with.