Throw all your god damn conspiracy theories out the window right now! They don't make sense. No way in hell would Valve ever release that source code in order to have a plausable excuse to postpone the game. That source code represents millions of dollars, and compromises the very security of the game itself. They can push the date back with a simple e-mail to bluesnews and we'd be pissed, but we'd still buy it.
So the heart of the matter. Why was such a great effort put into stealing the source code? Well, I remember reading that Half-Life 2, singleplayer or multiplayer, requires authentication to play through Steam. For the first time ever, are we presented with this requirement to be online to play alone. This was introduced for obvious anti-piracy reasons. BUT EVERY GAME GET'S PIRATED. However, not every game's multiplayer get's pirated. This is because of authentication required to play online, such as the WONID for Half-Life (which never got hacked to my knowledge, and if it did, it was only for the hardcore hacker). So Valve put their mighty foot down and said you must authenticate to play our game, even for the singleplayer. And so the warez community is in dispair, and some individual, perhaps a group, decides decisive action is needed to be taken if they are going to play this game for free. Thus the code was stolen (and a lot more if there's a playable beta out). There was even rumours that there is even more then was released in that beta. Now with the code and some (all?) the game content, Half-Life 2 singleplayer does not require authentication. The source code itself could also provide guidelines for overiding the authentication in the final game, which is why Valve now needs to modify it like crazy, hence the delay.
I know I'm stating the obvious here to some of you, but there are a lot of people out there who just can't seem to see straight on this one, so I had to say something.
Anyway, this has become one of those long posts I don't feel like reading so I'll stop it here.