Thing is, botters and RMT will always find a way to get hold of commodity items in order to attempt some form of price fixing and economy control.
In FFXI you could see RMT at the the Auction Houses all the time, and know (from looking at the sales history) they were buying up say all the black sole stocks so that they could pass on to a crafting bot/buddy to turn into sushi to sell.

If they find it harder to get hold of an item by simply buying it (which is an argument appearing against having some form of direct instant purchase like the AH system in FFXI), then they will just get more bots/RMT to go and fish, mine or kill the mobs that drop an item the want (over and over and over....)
They would definately not be put off by having to have some of their group stand in each ward in each city, probably using some hack or whatever, in order to buy the item from a retainer (which is effectively what they are doing right now) rather than doing it from the counter. Just my two pennies on this argument. Not saying that I am right, lol.