This doesn't directly apply to indie games, given that they tend to need less power, but I think the Mac gaming scene is largely dead because of cost and lack of customization. If you're trying to build a gaming machine, you're going to pay out the nose for a Mac of the same power as a PC, and you won't be able to do anything to the machine once you get it. My wife used Macs for years and years, but after she met me and saw all the stuff she was missing (and how much more she was paying), she switched to PC and never looked back. Now she hates Macs even more than I do, which I find somewhat amusing. But it strikes me as relevant that the things cost as much as they do. If you're buying a Mac, it's probably for a very specific reason, otherwise you wouldn't be shelling out that kind of money for something you could get much cheaper elsewhere.
1) I dispute your notion that other PCs are much cheaper than similarly powered Macs. Pick a Mac of your choice, then go to Dell, HP, or any other large PC retailer, and build a machine with similar power. It will come out very close to the Mac in price (the Mac might be a bit more expensive, but generally not by more than $100).
2) In terms of customization, it is true that you cannot swap out the motherboard or processor (in most cases -- many processor upgrades have been possible in the past, though they tended to be expensive thanks to custom parts needed); but you can swap out pretty much any other hardware. You can add more RAM; larger, faster hard drives; better or more video cards; &c. And modern Macs will run Windows, either in virtualization (side-by-side with Mac OS X), or on its own (Apple provides Windows drivers for the hardware as part of BootCamp).
3) I do not believe that either cost or customization have anything to do with the supposed dearth of independent Mac games. For starters, most indie games that I have seen are significantly less intense than AAA titles. AAA studios can afford to bang the hardware, and push the envelope -- they have tons of developers, and money to buy lots of hardware, and if their title pushes the envelope today, they can be confident that everyone will be able to play the game in a year or two, which is fine, because they have to money to go on without making sales. On the other hand, indies tend to be small, and the budgets tend to be tight. Their games need to do well from the get-go, and they probably don't have the money to buy the newest and shiniest computers every year. Though you already admitted as much in your own post.
Honestly, I believe that this supposed dearth of Mac games could stem from two things. First, the Mac market is small. Second, most Mac users did not buy their computers for gaming. There is a segment of the Windows PC world that buys computers specifically for gaming. Some of them get really high end machines, and many of them get good to moderate range machines. But these people are going to buy every game that comes out (more or less). If this group makes up only 5% of all computer purchases, it still makes up nearly as many potential gaming clients as all Mac sales combined (about 6% of computer purchases). Coupled with the fact that most Mac users are not gamers, there is little reason to make the game for the Mac.
As to having nothing to do with your computer once you get it, Macs are common in video editing contexts, and in many scientific contexts -- the ease of the Aqua GUI, combined with access to Unix command line utilities makes the Mac OS a good choice for scientific work. Macs are also just as capable of running a word processor, an internet browser, or a spreadsheet.
Finally, I disagree with your basic assumption -- that the Mac gaming scene is dead. Many AAA titles are ported to Mac, and there are many indies that sell Mac games. Ambrosia Software is still alive and strong, after 10+ years of publishing Mac games. Macs will play most of the really popular games (WoW, the Sims, &c), and even if they don't work with OS X, Macs can run windows.
Now, you are welcome to dislike Macs -- I really don't care, I'm not a fanboy. I prefer Macs for myself, but would never try to push them on other people. But if you are going to bash them, please do so without making things up, or repeating the party line of anti-Mac zealots.
xander
