When Macs go Intel, it won't necessarily make games easier to port, because the part of code that talks to the hardware in Windows is, more often than not, DirectX, the API (application programming interface) that allows developers to write code that talks to a uniform interface regardless of what the underlying hardware is.
OpenGL is also an API that talks to 3D hardware, but it's an open standard. So if the video card manufacturers support it, you can write code against it. NoLimits, Doom 3 and others use OpenGL, so the port is a little easier because (with exceptions) you don't have to rewrite all of that graphics code. It's not as simple as recompiling the program for the different CPU, but it is easier.
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