The problem with that, sourceninja, is that the Macs that cost the same as game consoles have crappy GPUs. The $600 Mac mini, the only Mac that even approaches console prices, has an Intel GMA shared graphics processor, which sucks and can hardly play any games. If you want to look at Macs that are at least somewhat capable of gaming, the cheapest one is $1200, and that's an iMac with a Radeon HD2400XT?not much of a graphics card at all. The $1500 iMac has a Radeon HD2600 Pro, which is probably about comparable to what's in an Xbox 360... but it's $1500. Meanwhile, the cheapest Mac to have an 8800, the 24" iMac with an 8800GS (probably about on the level of the PS3), is $2000.
These might be acceptable to people who use their computers for all sorts of stuff, especially work-related stuff, and who only game incidentally. But no one is going to go out and buy a Mac specifically for gaming (well, some people might, but it would be pretty dumb!).
Besides, in order to give Macs console-like consistency, Apple would have to stop putting Intel GMA chips in their cheaper computers, making them even more expensive. And more importantly, they'd have to get a bunch of developers on board. It's technically possible to do what you propose, but it'll never happen. Apple's tried to get game developers interested in them in the past (Halo was first announced at a Macworld conference!), but the developers inevitably lose interest and leave Apple because Apple's just not committed to putting adequate gaming-grade hardware in all their computers. This is even more true now that they're using Intel graphics instead of dedicated graphics in all their computers.