Probably because in Quake 2, they put their name "id software" on some dog tags in the intro movie or something. And dog tags are actually I.D. tags, so I can see the confusion.
I still like saying I.D. software instead of "idd software" for some reason, also.
It's delayed because the game isn't "done" yet, according to that John Cook chatlog on Planet Half-Life.
http://www.planethalflife.com/screenshot.asp?src=/images/screensnew/johncchatsteam.jpg
Hmm actually Valve said there were only a "few" things they wanted to add in, but they didn't have time. They've stated in the past that Half-Life 2 is really up to par with what they wanted to do. I'm sure it's going to be a very polished and super-detailed/thought-out game.