Here, like in the states, you can certainly get comparable systems cheaper, but at the "retail" pricing level they are all about the same still. Obviously most PC systems at this level come with a warranty, adding to value. There is certainly a bigger gap now than there was in 2008 when looking at price and features.
I wasn't quite sure how the comparisons stacked up in the UK, as the pricing is higher from what I've seen. But I've never pulled them up on UK pricing only, and made a side-by-side cost comparison either, as I really didn't have a need to.
I didn't even bother mentioning the warranty or hardware options available on the PC side, as I knew you're aware of it. But it does make a difference in corporate purchasing environments, as they want a single service provider and are willing to pay the increased costs to get it vs. 3rd party upgrades and multiple support requirements that follows if it's not necessary.
For home or independent pros (anyone on tighter budgets), that's not as much of an issue, as the financial aspects will dictate decisions.
But the value the earlier MP's offered ('06 - '08's) is no longer there in the US, and from what I understand, has followed suit in all markets.
Without knowing the true customer base for these systems it is hard to even guess, I wouldn't be shocked by any number be it 100,000 or 10000.
No, we don't know the real numbers, and it could be anything. But my point is that I'd expect it to be falling, not increasing, as the current systems have lost their value given the higher costs and for some that research them thoroughly, the issues are making them unattractive as well.
I'd guess the majority of users are buying them for audio, final cut or are artists who are accustomed to or want OS X and Apple's way of thinking. I guess some appstore developers use them, but I would think most aren't. They also have a place in academia still. I think Bubba Satori was right with his comment in the other thread that it'll be users who leave, Apple won't drop their pro software, but it may not be as enticing as it once was.
They do still have their place and users interested in them. Either by preference or necessity (i.e. extensive software investments). I also agree with
Bubba Satori that the customers will be the one's to abandon Apple, not the other way around. Apple will drop it only when it's no longer financially viable to them.
That doesn't mean pros won't have any ability to use OS X however (excluding Hackintosh means). I didn't do well to clarify there, sorry.

Given Apple's way of thinking, it seems most likely that they'll shift the focus to the iMac and equip it with LightPeak to handle the drive throughput requirements (maybe a few other devices may develop LP based products). But the general impression I have, is they want thin, attractive systems that use external devices for expansion. LightPeak + USB + FW will provide that to their way of thinking IMO.
OS X being available to PC's is another option (keeps those using OS X based applications buying them - Apple's software products, when they
must have PCIe slots). But the iMac direction is far more likely I think, rather than either porting OS X to PC's or MP's continuing on with desktop processors.
I think something else to bare in mind when discussing this stuff is that digital media creation is growing fast and there are a lot of creative types (many young and learning on Macs) who (will) need powerful, stable, reliable, systems but have no real technical knowledge when it comes to hardware and it is very easy to keep going with what they know and just buy the Mac Pro that fits their budget. There are also plenty of other reasons to deal with the negatives and still buy these systems. The things that drew people to OS X and Macs in the first place.
This is another reason I feel the iMac for professional use is the direction they're headed. PnP to the ports and load drivers = really simple, and doable even by the least technical people on the planet.
