My guess is that HL2 is more or less ready to go, and that what is holding things up is all this Steam nonsense. If there were still significant fixing to do on HL2, enough so that they could not make their release date, they would have known long before now.
The whole Steam project smells of nothing so much as a last-minute idea that grew, as software projects often grow, out of hand. It's called "creeping featurism", and it most frequently happens when someone who doesn't listen to his software engineers is calling the shots.
You are so wrong on so many levels. There are those of us who remember back in 1999 Valve was talking about a network of gaming isps called Powerplay. When they were discussing it a lot of what they were pushing sounded suspiciously like what Steam eventually became. Also, remember the first Steam beta? it was like 3 years ago. And remember that second Steam beta? That lasted for like 18 months. Yeah, completely a last minute idea.
The second account you're wrong on is that, guess what? VALVE LIES TO PEOPLE BECAUSE IT HELPS THEIR MARKETING! You're talking and thinking about HL2 more than you are Doom3, right? Why? Because of artificial contraversy! They had to wait for the ATI contraversy to die down before they could announce the delay so that the delay contraversy would have its full impact. HL2 is NOT ready now. No one in the gaming industry with half a brain thought valve would make this deadline. When I heard it announced at E3 I knew it wouldn't make the deadline.