There is no need of an AH, and this is why:

a) A waste of developer time when there are other broken mechanics that require much more attention.
b) It is redundant to place a buy/sell system on top of an existing buy/sell system that fundamentally works the same, which only has purely aesthetic differences.
c) A lack of in-game content. People are not buying and selling when there is nothing cool to buy and sell.

It is not infeasible to learn and adapt to something different in a game (something we humans evolved doing, don'tcha know.)