but more chips are on the way oh yea of little faith...
and there are more ways to get faster than simple clock speed and we're already doing it - multicores, multiprocessors. There will be another leap in technology over the next 3 - 6 years mark my words...! There's more than one way to skin a cat.
2nd, the main reason macs have been traditionally more expensive besides their generally superior hardware design and componentry (note I said TRADITIONALLY as in GENERALLY) which does account for one factor of the expense is the low yeild rates on PPC's which has made them more expensive as they have in honesty tried to keep up with Intel chip makers over the last few years. Now that the processor aspect of the design is cost wise on a level playing field with other hardware companies I think we will see a much more cost competitive Macintosh. I wouldn't expect them to compete with run of the sawdust mill cheap as chips PC's but certainly with the more reliable brand name assemblies.
Personally, I would rather have a Mac running such a system, even if it is slightly more expensive. I mean a few hundred dollars. If it's vastly more expensive that's another story but as i said, the cost difference between macs and PC and the benefits of purchasing MAC for that smaller cost difference is going to improve once the intel chips start shipping. I suppose only time will show if I'm right or wrong on that.
Why not have everything plug into MIR hardware? Because you can update software but not a box (not as easily or cheaply), software is cheaper, scalable to the budget of the user, can't afford a real time system (when it's possible one day) then you can buy the next best thing and render offline, and of course, it works the other way, the same software, with a new hardware/faster system etc will run if not straight out of the box then relatively soon after the hardware release getting potentially massive (relatively) speed increases overnight without the user having to buy new "MIR" box. Try to sell your "old" MIR box not so easy in a sellers market I would bargain, unlike a used PC or MAC which can be put to heaps of different uses when selling second hand a lot easier to shif I would imagine.
The nature of MIR and the fact that until it can render in full quality in real time, no system will be "it" it would be best to stick with software at least, and who knows, what kind of future developments will further increase the processing demands of MIR so even then...