One thing to keep in mind: It takes ~2-3 Months for most companies to produce their shippable product and get it out the door, especially considering that they (SE) develop for so many countries. Assuming that they are working on the code now, and want to determine character balance, and play methods people like/don't like. It will be 2-3 months after the release before they know for sure what they want to do. So, at that point we are already sitting 4-6 months out from the original release before they can get something in our hands (by physical media). Put in the fact that they will be producing the disks for the PS3 around that time as well (add the Sony overhead for production on that), and yeah, 6 months is actually a pretty tight schedule for them. While it would be nice for us (which I think is why they stated they *might* release a class or two early), it is very unlikely we will see anything more than bug fixes before March.
As well, pushing things out too fast will cause two major problems. Chance of defects go through the roof the more you rush (there is never enough development time), and customer expectations are higher the faster you release (seems it should be the opposite, however, the faster you do it, the faster people expect more). These are some pretty standard tenets (and many people in these forums have stated them in their own way).
So, here's to hoping it's March:).
(On a side note, if it is released in March, it will be free for the PS3 users. That's their carrot to buy, while the PC players carrot is the early release and chance to develop earlier. PS3 players will have an equal (or nearly) chance to explore the new areas in the expansion so they don't feel left out, or shafted that they have to buy 2 games just to play.