Hell, if it's a difference between $5 million and $40 million in profit, I'd sit on the game for a couple of months too. Not that I know which orifice you pulled those numbers out of.
I think there were probably a number of factors going into this delay. I'm sure the game will benefit from some more tweaking and polishing and bug-testing. I'm sure Valve wants to wait and let ATI and NVidia get their latest cards and drivers a little more stable. I'm sure Valve would like Steam to be tested a little more thoroughly before HL2 comes out. The fact that D3 won't be coming out until next year, and HL2 will be the major game release of the holiday season.. the probably played a part too. Delaying release a couple of months will probably result in a lot more sales.
I really don't care. I have other things to do. I'm not going to sit here in front of a blank screen, moving my mouse around making shooting noises with my mouth and pretending
that I'm playing HL2. Valve has a lot of good-will in the bank from HL1 and all the mods and add-ons and extras they released for free. I'll get on with my life and play HL2 when it's ready
I'm sprawled across the davenport of despair.
It's the land of the brave, and the home of the free, where the less you know the better off you'll be.