I think the reasoning behind the manipulation is to give a reason for evil. It doesn't really make too much sense for one guy to think to himself "oh I'm going to dominate the world with a horde of undead". There's a need for an outside influence (and in that case an extravagant one).

I know thats rather simplistic, but giving the old god the influence they do is a easy way to explain motive without the complication of going in depth. I mean not many folk are going to read the explanation in quest text. (especially atm when you have some opportunistic gnome trying to gank you when you hand in, then you try and fight back and that NE druid that you thought was afk springs to life... then your dead!

If your going to explain Deathwing's motives with out an old god, it makes no sense "I don't like what the titans told me to do - RAWWWR".

The alliance vs horde thing fair enough it seems cut and dry with a good and bad side, but part of the reason I like Warcraft so much is that it blurs the boundaries so much, if you play horde you think alliance are evil, and like wise if you play alliance. (especially now).

In all honesty I wonder how they can keep the horde v alliance going, its starting to stretch believability that we're still fighting what with all the argent dawns, cenarion circles, etc kicking about.

I hope we do though, I really hate gnomes!