aparently the api mac uses is just not nearly as good as directx and the entire process to emulate games like WOW to play on it leaves you lacking.
A problem with Mac OS in terms of games is indeed the API that the operating system supports.
Wheras Windows supports not only DirectX11, it is also capable of handling the very latest OpenGL versions - through a process as simple as upgrading the Graphics Card driver. Somewhat current Windows boxes as such are going to be sporting DX11 and OpenGL 4.2 support.
XP machines will be limited to DX9, but can still run OpenGL 4.2. Linux machines handle 4.2 as well.
Mac OS machines however will have no DirectX support (for obvious reasons), but more problematically - only OpenGL 2.1 support if its Snow Leopard. Or OpenGL 3 support for Lion & Mountain Lion.
Newer revisions of both are used not only to add more types of graphical shaders, but to improve performance through more effective rendering and programming techniques. DirectX 11 in WoW for example is one of the top priorities for improving performance - and Mac OS simply does not have any way to enjoy the same efficiency improvements.
In the end, not only does Mac OS require developers to code against a completely different API - it requires them to code against a different API that is
obsolete.
The second problem is one of optimization. On Windows & Linux, new revisions of drivers are released monthly whose job it is to remove glitches (many specific, based on individual titles), but also to enhance performance and efficiency. In most cases, these will be only a few percent - anywhere between 3-6% tends to be more common. But 10%, and even extreme cases as 40% have been known. Mac OS, due to Apple's display driver model, simply does not enjoy this luxury, and will be behind the competitor systems even on the same types of loads.
Of course, some houses just employ a wrapper around the whole thing - which throws performance out the window; simple to implement though.