Since the MoP pre-patch, area looting in the world is transferring the loot from only the corpse the player interacts with. No loot from the other corpses is transferred to the player, and all other nearby corpses become “unlootable.” So, if you round up a pack of mobs, there is a miniscule payoff. Please note: area looting seems to be working correctly in instances. I tested it in Karazhan.
Update: I went to Deepholm and killed several large packs of troggs near Stonehearth. Loot received was silver only—no items or cloth—which indicates a problem. I toggled off Auto Loot, but that didn’t change anything.