I think captain blue said it, but I think the reason we won't see Portal (or anything out of Valve) on the mac has to do with a grudge, or something, Valve has against Apple. I don't know much about it, you'll need to read up on it.
Besides, Apple has never targeted the elitist gamer market. That would be Alienware :P
If Apple wanted tons of games and software instead of a sturdy OS, they would have forced their OS on to every OEM in existence, and use the money they made from doing that to wipe out any competition.