Let's see...
For starters, Gridania (a.k.a. a 'starting city') would not be an absolute GHOST TOWN a few months after release if there was a world-wide AH. Since Uldah had all the coblyns in the beginning, it gained the economy once everyone started playing there. Since the economies aren't inter-connected worldwide with an AH, Gridania and now Limsa Lominsa are both becoming pretty vacant.
What else... oh yes. It takes about 1/5th the time to actually put an item up for sale.
