A minor rebuttal...
Buying a Mac -- or a PC -- for gaming has become a waste of money. You are -always- better off with a console (Xbox 360 and/or PS3) for gaming, because you NEVER have to worry about the specs or if the next great FPS will run on it: They always will.
Apple's hardware is not very upgradeable and especially in the graphics department, it is always behind. It's nice that you can add tons of RAM, CPU power and hard disks to your Mac Pro, but you will never be able to use the newest generation of graphics cards. And for hard core gamers, that effectively ends the discussion.
The next killer argument for the consoles and against PCs/Macs for gaming is DRM. The only copy protection consoles use is verifying the original disc. On Windows, in most cases some horrible DRM driver will be installed, and those drivers come with many unwanted side-effects for the user. Sometimes, they prevent other games or software from being installed. In other cases, they work like trojan horses (remember Sony?). And in other cases, they could not be properly uninstalled without killing the operating system. Then those drivers and their activation mechanisms usually do not allow you to sell the game when you no longer want it. (And I might add that re-selling a game or software in general is perfectly legal in most countries on this planet.)
You won't have any of these problems with a console.
What you say is true but I prefer to use my MacBook pro instead of a console. Why?
1. I can play anywhere as long as I have an outlet. With a console I am tied to my home and I am someone who is always mobile.
2. A good portion of the games that come out on consoles are available for the pc. (personally can't wait for SF4!). The only games I do miss are Final Fantasy, Tekken & Gran Turismo.
3. Because consoles always have the same specs, I never have to worry about requirements for the port. Most pc games don't have crazy requirements except the rare ones every few years that come out like crysis. I am not that hardcore anymore that I need to have all the latest & greatest. Since most of games are at some point going to have a console release they really never push the specs. They also do this because they also want to reach mainstream pc gamers to maximize profits. There is currently no game on the horizon that pushes the limits like crysis did.
4. I can do much more with my machine than if I had just a macbook & xbox/ps3.
5. I have to worry less about which game is for which console when it comes out.
6. For most games there is no online fees. With the xbox it's $50 a year membership.
7. Consoles generally have low quality hardware (ie red ring of death) because they make their money on software. With the MBP I have the best hardware I can get.
8. As was mentioned previously console ports are cheaper.
9. Maybe most importantly my girlfriend thinks it's childish to have a gaming console. I know, I know. But once you get enough stink eye looks you just give in.
If he's got the money for a mac pro then go for it. Though if you've got that kind of money for a desktop I'd recommend a MBP and replace it every 3 years and you'd have a portable gaming machine.