It's always amusing to see how worked up people get about computer manufacturers and operating systems, it's silly, especially when remarks are unfounded.
Right, to answer the question and offer some advice. If you want a Mac there are solutions for game development, then there are some out there. Your first problem is that anything DirectX will not work for you, because DirectX is a Microsoft product and it seems they won't strike a deal with Apple, which is fair enough as they're competitors. But rightly said Macs use OpenGL for gaming, though Macs aren't marketed for gaming, and only few developers make anything for it, but there are games availible for it, commercial and indie, you can even get Call of Duty 4 for it.
As for programming and development, you can use XCode, which I believe is free, it has C++ and other development tools for MacOS and you can download SDKs that will work with it, like Irrlicht or Ogre, which like DarkGDK are free, but unlike DarkGDK, are capable of using OpenGL and are Mac compatible. Personally out of the two I'd recommend Irrlicht, but check out for yourself, as they're both free you have nothing to lose.
But will your products only run on a Mac? Well, nab Windows XP and use Boot Camp, so you can run two operating systems, but if you don't want the effort of doing that, run Windows under a virtual machine, so you can get the best of both worlds, meaning you can transfer your code and edit where appropriate on the PC version, so you actually get both audiences.
Alternatively, if you don't mind splashing out a bit of cash you could try the Unity3D engine, which is a game engine designed for the Indie game industry and is very well put together and was developed and a for the Apple Mac and only very recently has a Windows version been released (I tried the trial and fell in love with it) and the plus side is, it'll compile your game into the format of your choice, you can compile for the Unity3D web player, MacOSX and Windows and has a good set of quality settings. Download the trial and test it out for yourself, if you do, I'd recommend looking for 'Lerpz Tutorial' as it's a fantastic step by step beginner's tutorial that explains things really well.
If you're buying a Mac only because you're intresting in movie editing, Windows is still good for that purpose and there are applications for it that'll do the job. I should hope there are other reasons for choosing, if you buy one, then well, don't think your game development option is stunted and nor is your audience.