I think they will release it in 2011 because it IS a big deal and lots of people want it. The problem is, by the time 2011 comes around, less people may even care about HL2.
If it wasn't for Left 4 Dead 1 and 2, we'd be enjoying episode 3 right now, but dont count on it until 2011. Episodic gaming suppose to be quicker than sequels... BS!!!