Perhaps the reason you're resorting to vague name-dropping is that you know I'm right Jerome? [:D]
An alternative answer: perhaps that's because they don't care about the price, given the budgets they're dealing with? [[;)]]
cuts, if the price really does work out - even after figuring out how you're going to get the audio out of those machines and clocked together, and also sticking FireWire hard drives on them - then I agree you're going to do better with three minis.
But while a stack of those things has sex appeal, my educated guess is that it doesn't add up, that you're going to get a lot more mileage out of machines that don't have such a minimalist design. 2GB of RAM is a waste of a machine, they have slow hard drives due to their lack of cooling, and they don't have PCI slots (he says after arguing against PCI due to the constant obsolescence...).
I don't like dealing with Windows machines when something goes wrong*, but they do work well in between, and you can put together an equivalent machine to the Mini that has none of its shortcomings for less money. The Mac Mini really is more expensive than comparable Windows machines; the Mac Pro is less expensive.
Note that I'm not seriously arguing with Jerome. He's obviously put together more than one very solid rig with those machines, and of course they work well. I just wouldn't spend that much money on half-assed computers - especially now that 64-bit memory access is just around the corner (as are considerably more powerful machines, according to rumors).
* The two times I've really got into trouble with my Windows machines, I posted to VI-Control, asked around, searched the net high and low, and in one case even called the people who sold me my custom Windows machine (www.VisionDAW.com). Nobody was able to sort me out, and these are people who use Windows every day. I finally got there on my own, but it was ridiculous both times.
Point being, if you'd rather deal with Macs because of that, I fully understand. [:)] But I personally would stick with Mac Pros.