I don't think anyone is surprised that Skyrim's next DLC, Dragonborn, will be releasing on 360 considerably ahead of PC. Which is to say, tomorrow. At least we've been given a general ballpark this time: the quote is "early next year" for the PC release, which could mean as soon as January or as late as maybe March. Assuming a 30-day exclusivity contract with Xbox and a similar delay to what we saw with previous DLC, we're probably looking at the first or second week of January.
The official announcement can be found on Bethesda's blog .