That will be well good, when games are released at the same time for both pc and mac. I expect it will be a while yet though
EA announced they will start doing it in July, and id said they will have more mac related announcements in august.
I suspect it will happen quicker than you think, both companies said it was very easy to port their games to the Mac, you gotta remember its based on Unix, so all apps are self contained with the minor exception of a few content packages here and there. There is no system registry, all resources needed to run an app are in the app's folder itself. Plus since apple is no longer PPC based I can only see it being easier and easier.
Apple also offers a full range of Nvidia video cards as well, and ATI announced like 1.5 years ago they will released dual platform video cards that run both on mac os x and windows from the same card. Meaning a Mac gamer could go to a computer store and buy an ATI card and it will work in both mac and pc no problem. Of course ATI hasn't released every model that way but that is probably because mac switched over to EFI with the release of their intel machines.
I can only imagine it getting better and better especially with all the crap that MS pulled with vista. it just leaves a bad taste in your mouth.