Perhaps SE is waiting to implement the same concept as that of D3: Real money AH? They would receive a certain amount per transaction and could potentially drive gil prices down enough where it would not be profitable to RMT for profit? I have absolutely no basis for this and am saying it halfheartedly, also, D3 requires a constant net connection as an attempt to cut down on the problems D2 had.
Maybe SE can come up with something to squelch the RMTs this time around. It was interesting to log onto POL and see the mass bans of suspected RMTs though. I wonder how much money they have made just in the lifetime of FFXI.