So... is there any point to multiplayer?

Now here's a concern I wasn't expecting to have. Why play multiplayer instead of solo? Specifically, why play PUBLIC multiplayer, since of course running your friends or little sister through the game is its own reward. But what about the rest of the time?

I played Diablo II extensively, which is to say obsessively, and in that game you had to play multiplayer to efficiently level or farm. Why? Better XP, more drops. The dynamic worked like so: The players who had optimal builds and equipment (who could actually still kill stuff in 8-player games) benefitted from the extra XP and the higher chance of something awesome dropping, while the tag-alongs who were in a bit over their head benefitted from the XP and well tagging along, hanging back a bit and grabbing leftovers. Playing together with strangers still made sense for everyone.

So now. I greatly appreciate the private loot, I think it's a much better idea that the goods be split equally rather than always go to the closest/fastest clicker. But after running through the beta with each character class and then having run the SK a few times in public games (because that seems to be all people do in public games, which is fine by me), I can't help but notice that I don't seem to get more/better loot, and I don't seem to get better XP.

So what am I getting? I guess if I were playing a character who can't kill things that well by myself (*cough* demon hunter), then tagging along still speeds up the process. And of course right now, I'm honoring my sacred duty to play public games as part of the beta. But that aside, where's the incentive to play public for those who can tear through the monsters? Why not just tear through them twice as quickly in a private game, since in the public game those monsters are NOT dropping twice the loot?