[ZoFreX]

There was, and is, a lot of FUD about the HL2 leak. One of the confusing factors is that there were actually multiple leaks - at first it was "they just stole some code which no one can get to compile" and by the end it was "there are playable levels". Basically everything Valve had at the time was leaked it seemed - there was a huge amount of assets, a fairly complete engine, multiple levels including bits of the now-infamous E3 demonstration.

The reason it was delayed is, quite simply, that it was nowhere near ready, and I think this would have happened with or without the leak. Valve aren't exactly renowned for releasing on time, there's no way they would have released an unpolished game just for the sake of a deadline.