Do you count the fact that due to their Intel architecture, you can install Windows Vista on an Apple MAC?
If you do, then obviously a MAC has more software available to it.
In fact the MAC has three ways you can run windows software on it.
With a dual boot, so you can shutdown the MAC OS and boot into windows.
Parallels visualisation software allows you to create a virtual machine into which you can install windows and it will run within a window not 'knowing' it's not the only operating system running. This gives one near equivalent speed (theoretically) but without the need to reboot and with some MAC OS integration.
Crossover is a program by codeweavers which allows one to install a Windows program directly 'onto' the MAC OS, allowing the program to execute as though it were running in Windows. The advantage is that you don't need a Windows license to run it. It also mean tighter MAC OS integration, but at the expense of speed and stability. Only a certain number (growing all the time) of Windows programs have been tested and are know to work with Crossover.
With all of these options the MAC does windows software well, and would be the clear winner if not for one thing. Games.
In my post I'm going out on a limb.Although Apple provides drivers for Window XP, I am generally talking about Vista here because its the latest release. Further more, Apple states that it does not support Windows on it machines (fair enough since Windows is more or less the competition). This means that none of the three options could be said to run Windows Vista optimally. That my friends, means everything to gamers.
The only way to get you OS at peak performance is to have the latest high performance support files (drivers for PC's, kext for MAC OS) and to have the OS unhindered (by running in a virtual machine – Parallels, or with api emulation - the way Crossover fools widows programs and the MAC OS into thinking they were made for each other).
With Apple not supporting Windows on a MAC we have to say that for most people its not going to run as well for games.
There is also the confusion that if you install Windows on a MAC, you'll need one copy (license) for that machine. Forgive me for the blatantly obvious but that makes it a MAC that is also a PC. The argument here is MAC or PC. Incidentally the term P.C. Originally meant 'Personal Computer', now it generally describes (as in these posts) 'machines which run Windows or Linux'.
So if we talk about an Apple MAC of the current line up, it can run windows programs and run them well, but I say it's still not the platform most used, and most trusted for games. And the are thousands of games out there.
There have been good speed tests of MAC's running Windows Vista but those normally have Vista installed and tweaked by experts.
Gamers need Windows unhindered, therefore software availability still goes to PC's.