I was wondering the same thing. It's been over 8 years. If you were at ALL interested in Doom 3, wouldn't you have it already?
I have my old CD copies plus I have it on Steam where I picked it up maybe late 2011? It was on one of those ridiculous sales, so I have all id games from Doom 1 through 3 and Quake 1-IV (even though IV wasn't totally theirs) and Rage, all bought for at least 50% off current price (which was usually a lot less than the original price). I got them there for convenience, as a lot of the older CD-based games have CP issues with modern and/or 64-bit OS.