I think damocle's is right on the money.
If the game wasn't finished then Valve would have some idea of what was left to do and at least an inkling of how long it would take to finish. I can't think of a single thing that would have Valve tentativly sticking to a release date right up to seven days before it except for something beurocratical.
If they had spotted some bugs, even with Steam then they should know if it's closer to a 2 day job or a six week+ job. Valve probably did what we always ask (and never expect them to do) and completed the game before announcing it. Legal matters and talks with Vivendi is probably what lead to the slippage.you can't have your cake and eat it too.
What's the point in having your cake and not being able to eat it?