So, I'm thinking the reason for the Xbox-version appearing on the market before the PC is that Obsidian (and/or Lucasarts) are afraid of piracy.
Let's face it - as soon as the PC version appears on the market, it will also appear among the pirates, regardless of whatever copy protections they use (look at HL2).
So, by releasing the console version some time before the PC, Lucasarts hopes that the people who own both an Xbox and a PC will buy the Xbox-version instead of waiting for the pirated PC-version.
OR
They are trying to implement some new and improved copy protection system, and are working to eradicate the bugs from that.
At least that is my guess - I have come to believe that most of the times when a game has irregularities with the release date it has something to do with copy protections...
Oh well. February is only a few months away....
