DVD drives are cheap as hell, so are cd-writers. it would be a waste of $$ to buy a vanilla cd-rom anymore. I got a dvd/cdrw combo for only $30 after a rebate, same as a cdrom would have cost me. And I would think any computer old enough to not have come standard with a dvd player probably wouldn't be able to play HL2 anyway.
And why would you want only one cd/dvd type drive? I have three, it's great, no swapping stuff all the time to play music/games/movies. My fourth slot is saved for a dvd-burner when those get a little cheaper 
UT2k4 will come on either 6 cds, or a 2 dvd special edition (2nd DVD is mapping/modding video tutorials & extras). I'd rather have the DVD for games this big if only because it's less an annoyance to install and keep track of it. Hopefully more big games will follow this trend and at least give you the option of getting them on DVD.
Has there been any talk of HL2's size, anyway? It's kinda hard to know, since we can't be sure what will be included beyond the 1player game (though that's probably 2-3 cds itself )
