@fudge

That's not really fair and you know it. You're speculating on something based on nothing but a few sentences that's three patches and a whole expansion away. I can play the baseless speculation game too:
The Alliance walk into Orgrimmar torn by civil war, civilians slaughtered in the crossfire and the majority of Horde forces in disarray (Garrosh has to have some forces loyal to him).
Perhaps Varian takes the moral high road (like that interview with Metzen suggests he will) and realizes that even his old enemies don't deserve this slaughter, and that it might actually be in his own interests to have someone in control of the Horde who isn't a raging warmonger willing to sacrifice his own people for personal glory and unnatural power.
Perhaps Thrall is racked with guilt and anger, seeing his own city destroyed by someone he put in power, perhaps Thrall is in need of rescue or serious help (he always was pretty trusting). Perhaps Thrall, when all is said and done, refuses to take the mantle of Warchief, guilt-ridden over what Garrosh has become, or furious with those who were loyal to him, or because his own family must now take precedent over a Horde that didn't much seem to mind that he was gone.
Perhaps Varian knows that the Horde won't follow a puppet leader and aids Voljin to becoming warchief, logically picking the much lesser of two necessary evils.
Perhaps the Alliance walks out proud, united, and morally justified, while the Horde has to sit back and wonder how the hell it dropped so low that the Alliance had to come in and save it.

Jaq is exactly right that the Alliance have room to complain after Cata, this can't possibly be argued. And then Blizzard came out roughly 100 times and said "we hear you, we understand your complaints, we recognize that you are right, and we're going to address this in MoP", and yet people still complain about content that doesn't exist yet.