It isn't just the Windows versions that play a factor, though. Medal of Honor: Allied Assault does state at the bottom of the page in the system requirements:
Compatibility notice: Intel integrated graphics cards, and ATI Radeon X1800 cards, are not supported.
Whilst The Witcher states for Windows machines that it needs NVIDIA GeForce 6600 or ATI Radeon 9800 or better, and only mentions integrated Intel and laptop graphics cards for the Mac system requirements:
Minimum system requirements: Windows XP, Intel Pentium 4 2.4GHz or AMD Athlon 64 +2800, 1 GB RAM for Windows XP, 1.5 GB for Vista, NVIDIA GeForce 6600 or ATI Radeon 9800 or better, 8.5 GB available hard drive space, DirectX 9.0c compliant soundcard
Minimum system requirements (Mac): OS X 10.6.8 or later. Processor: Intel Core Duo 2GHz+ Memory: 2GB of RAM Graphics: nVidia GeForce 320M (or better), AMD Radeon HD 6750M (or better) or Intel HD Graphics 3000, Recommended two-button mouse, or Apple mouse with Secondary Button / Secondary Click enabled.