Hopefully somebody wakes up and stops the vicious cycle.
Not going to happen.
I happen to like the direction the MP is going in (i.e. compact and super quiet), but I agree it's annoying that there's so little choice. They don't
really make a Mac for me either - I would have rather had the nMP form factor with the top-end i7 and nvidia GTX GPU. But it's unlikely to ever happen, even though countless users having been begging for such a machine for years.
There's only going to be less and less choice in the industry. I used to have no problem spec'ing out Dells and HPs with top-end components... it's ridiculously difficult now (without getting into funny-money "workstations").
There is a paradigm shift at work here.
First, as the world has gone mobile, 95% of individual computer users aren't even remotely interested in these type of machines. And the remaining 5% - the OEM's figure if they're that desperate for the hardware, they'll pay a lot of money for it. But obviously that 5% is not in Apple's business model. It's a sliver of an already small slice of pie. It sucks, but that's just the way it is. I'm thankful they still even have an MP in their lineup.
Second, when users do need serious compute power, more and more that will be done in the cloud. Not quite practical yet with rendering something like multi-gigabyte video, but that's where it's headed. What's too big to upload to the cloud can be off-loaded to local rendering servers. Those will eventually be replaced by appliance-like devices as well (they already are).
Steve Jobs was never particularly interested in computers as "computers"... that was Wozniak's thing. Since the introduction of the original Mac, Jobs saw it as an "appliance" (long-time Apple buffs knows about the "Hyperdrive" and how Jobs threw a fit about how he had explicitly had the Mac designed without internal connectors so something like that wouldn't be possible). Then came his Next cube with pretty much proprietary everything. When he came back to Apple, the industry was in the age of the computer "tower", and he knew that he couldn't simply wipe them from Apple's product line. But he tried, at least from our collective consciousness. We can all imagine him on stage, giddy with excitement introducing the '98 iMac, the G4 Cube, a string of laptops including pulling the MBA out of the envelope, and of course the iPod, iPhone and iPad. Honestly, how many memories do we have of him physically standing in front of Mac towers? When the original Mac Pro was introduced at WWDC 2006, Jobs left it for Schiller to introduce.
Again, it sucks that they can't find a few bucks out of their gazillions of dollars to have a couple extra Mac models even if they aren't best sellers. I've done my fair share of complaining about it over the years, but at some point, accept it and move on. You'd all like to think Apple will be crying when you replace your cMP with an HP Z-whatever, but they won't. The only reason they still even have an MP at all is because it's a halo effect product.
TL;DR: If you're interested in big upgradeable towers (or upgradeable computers for that matter), Apple is no longer the computer hardware company for you... it's either Hackintosh (as long as that lasts) or make the move to Windows. But jeez, just be done with it already.