I've simply got no idea. Do you know? Or you, Steve? Perhaps I'll ask John. "I've no answer for you," says John. "It should remain a mystery, like magnets." See, no one actually knows. It's convenient then, that Blizzard should have put out an "introduction to Diablo III" video (via VG247) for me to post below. That explains it. That explains it right up.
Related news: Diablo III will be playable - via mandatory internet! - tonight from midnight Imperial London time. So that might answer some more questions.
Come on then, let's have it. Who's being what class?
I am, of course, going to be the handsome, proud barbarian. (And in the game!)