I was reading the Diablo 3 Wiki, and it was really interesting. I may read the Diablo trilogy which looks to be quite interesting.
Anyways, here's why I am wondering if Blizzard may not even know their own lore:
Sanctuary is a basically Earth in Diablo. It's where all humans live. Heaven and Hell both fought over Sanctuary; neither ever managed to succeed in taking it. Eventually, like-minded angels and demons gathered with Inarius at Sanctuary, where Inarius created the World Stone (which shielded Sanctuary from the heavens and hells, where like-minded angels and demons who were fed up with heaven and hell could live peacefully together). Humans are "nephalems". Nephalems are the byproduct of angels and demons getting together and doing the nasty. Anyways, a byproduct of the creation of Sanctuary (or something like that), was Trang'Oul. Trang'Oul went unnoticed by Inarius (the brother of Tyrael), and taught some of the first Nephalems the art of necromancy. Trang'Oul comes close to a god-like state of power, but it's uncertain where he really stands... and it's unclear what he's doing (I don't know). It would be cool to see Trang'Oul in D3.
Now, here's some important information: The World Stone was altered by Inarius in an attempt to reduce the power of the nephalems. The first generation of Nephalems (one of which made by the pairing of the angel Inarius and demon Lilith) was more powerful than both of them, and they fought over being the favorite of their child. Ultimately the power of the nephalems brought Inarius to alter the worldstone to reduce the power of nephalems generation by generation. Lilith also slayed all the other angels and demons in Sanctuary (something like that).
Anyways, Trang'Oul is the major nasty powerful dragon who goes to the trouble of teaching Nephalems the art of necromacy. He is basically some big badass who helped the nephalems gain power and champion their world as heroes. And that's what Diablo is all about: The people (nephalems) fighting to champion evil (or any opposing force) which might threaten their existence. Necromacy is one of the first arts taught to them in order to give them power. In fact, the later generations of Nephalems had to be taught or coaxed into learning/attaining their powers (unlike the previous generations which just inherently could do magic and have power), so necromacy is one of the arts which is important to be taught.
So anyways, I think because of how important necromacy is in Diablo... I wonder why instead of a necromancer, we have a god damn witch doctor instead.
There's lots of cool lore to Diablo, an actual story line... and Blizzard is messing it up... maybe?
I used to love playing a necromancer in Diablo 1. I had an epic fight with the butcher and my Necro.
That mother dropped me my first Obsidian ring of the zodiac.