one thing to keep in mind here too, windows machines can also run OSX, right up to 10.4.6.
having just built a new AMD system, two cores running at 2.6ghz, 2 gigs of low latency ram, nearly a terrabyte of storage, two nvidia 7900 GT Superclocked CO's in SLI - it runs OSX 10.4.4 beautifully. oh, and it cost under $1000.
don't get me wrong, i love macs - love em. use 'em every day at the office, but the software set isn't there, running windows on a mac is buggy as hell, there are almost no games worth playing, and they're not affordable.
when Apple starts to allow third party vendors, prices will fall, and MAYBE, just maybe a level playing field will start to form.