That's true. The game's been repackaged for Mac and yet it seems that none of the listed Mac graphics cards can handle the game on it's ideal settings
I wonder how it plays an a newer Mac Pro tower?
Not much better. The Mac Pros have 3 generation old cards, aka radeon 5000 series. Although the 5870 beats the 6970M in the iMac by a fair margin, it's still considered weak by todays gaming standards.