Apple's hardware is by no means inferior to the offerings from other manufacturers, and the OS capabilities are definitely there for high throughput calculations. Despite this, gaming on the Mac has had relatively lackluster performance, as was exemplified in the release of Steam for the Mac. While titles are increasingly being developed for the platform, the performance of various games can sometimes be half that of the same title running on similar hardware in Windows.
As we described in Windows drivers, on the other hand, are highly tweaked for specific game titles., these issues are largely due to graphic driver immaturity, where Apple provides relatively minimal enhancements and focuses on stability instead of raw power and performance tweaking.
Apple is apparently quite aware of this difference and is trying to bridge the performance gap by working closely with Nvidia, ATI, and game developers to enhance driver development. In a recent posting on Valve Software's forums, a member of the Valve team commented:
Performance is going to improve as drivers are updated. I would expect modest improvements in short term and larger ones in longer term...We are making a lot of progress is identifying specific issues that need work inside the game and inside OpenGL and drivers. Apple, ATI and NVIDIA are all involved.
Lets hope this translates to more work being done by Apple on the core drivers, instead of the responsibility being primarily the game developers' to just tweak their software. We will see, but this indicates a potential upcoming boost in overall graphics performance on the Mac.