Once again, you have no idea what you're talking about. It's very common for Mac versions of games to have different publishers, and no, it's not because they're not as good as the PC versions.
The game was delayed quite a bit, period, for both platforms. Carmack thought he was going to release it not long after the GeForce 3 cards came out, and he had this to say about the Mac version:
We do run a bit better on a high end Wintel system, but the Apple performance is still quite good, especially considering the short amount of time that the drivers had before the event.And that was in the days of the G4, not the much faster G5, before good Mac drivers for the GeForce3 were out. The context of this quote is a MacWorld expo for Apple's release of OS X and inclusion of a GeForce3 card in their systems. John Carmack came up to demo the first public showing of Doom3 -- on a Mac.
That's because Aspyr's business is to port PC games to the Mac platofrm. They evaluate which titles they think will sell well, buy the rights to port the game and then port and publish under their own name.
What I find really interesting is your rabid defense of the PC as the superior choice. Feeling a little defensive?