Just took a screenshot from diablo 2, I don't have an inventory full of stuff yet since I just installed the game 1 hour ago, only gear I have is from some friends.
But just look at how much space the items in diablo 2 take up compared to diablo 3.
screenshot -
diablo 2 inventory
Unless the only things your put on your mules in diablo 2 were rings, amulets, charms and belts. Then it's clear that the reason you needed all those mules in diablo 2, were that items took up a lot of space. Something they do not do in diablo 3, in the same way.