I can't see a reason why a Mac shouldn't be good for game design too?! I mean, its just a fucking operating system, people should get over it and just accept that what they use might not fit the bill for everyone.
Sorry, no offense to you, but some people can't accept the fact that Windows, Linux distro of choice, Mac OS X, BSD flavor of choice or even Solaris, that they are all mature operating systems and some people just don't like Windows and use something else which they can use the best and like the most.