While I share everyone's frustration (I am a PC gamer after all), this XBOX360 exclusivity conspiracy nonsense is just getting silly. If all that were holding it up was an exclusivity deal with Microsoft, it would have released on January 04 or 05. Believing that the PC version of the DLC was held back until the PS3 version was ready is slightly more believable (though no less aggravating).
Remember that content (not updates) for Skyrim is developed on the 360, just like the main game was. Porting to other platforms (PC and PS3) takes time. It's not a set amount of time and the longer period that Dragonborn has taken to port to these platforms is more likely an indication of its size than anything else.
I'm not saying people shouldn't be irritated at Bethesda, but clinging to this exclusivity conspiracy is really not productive. People need to educate Bethesda of the foolishness of developing primarily on a platform that is 8 years old and technologically obsolete. And that says nothing of the fact that it's highly insulting to the most loyal (and oldest) members of their fanbase who supported them through TES III: Morrowind.