> The ultra-performance professionals ... often do their own builds and then keep upgrading them.
I think this claim stands in pretty stark contrast to the history of Apple products in the professional graphic/video sector.
Even for people doing stuff like CAD that is less sensitive to image quality and more performance-oriented - nobody at a company of any real size (say >25 users) assembles their own hardware. I'm sitting two feet from an HP Z400 workstation that my (architect) father-in-law snagged for me when his company upgraded their CAD workstations.
The reality is that assembling PCs, debugging them when hardware breaks, etc is not free. Once you approach a certain scale (I would imagine this is roughly around the point of a single tech) it starts becoming worthwhile to externalize the cost instead of hiding it in salaries. For a price, Dell or HP will make sure that you don't have to worry about your hardware. If you hire a bunch of new people, a bunch of new boxes will show up tomorrow. If you have a PC crap out, they'll get it back up tomorrow.
Of course they do charge for this, and they make a profit doing it (i.e. they charge more than it actually costs). Once you are at a really huge scale, it might be worthwhile to bring it back in-house and have someone do it full-time. But like any managed service, it's a viable proposition at certain scales. You buy Amazon AWS instead of running your own servers, a lot of businesses buy HP or Dell workstations instead of worrying about it themselves.
Power-gamers are pretty much always individuals, who (like tiny startups) are price-sensitive and build their own hardware. When you don't have an income stream tied to the product, it's worth spending an evening building it yourself. Although this still assumes a power-gamer with some decent knowledge of hardware. First-time builders have a bit of a hump to get over, and beige boxes sold for family PCs drastically outnumber the power-gamers.
Still though, to the more general point, Apple still has some pretty serious mind-share in the professional market, although it fades year over year especially when they're pushing shit like the trash-can Mac. I think it's premature to say that Apple can never succeed in the professional market, especially given their historic inroads in that market.
But again, they do themselves no favors by not upgrading their hardware. The current base model Mac Pro GPU uses the workstation version of the Radeon HD 7870. The high-end model uses the workstation version of the Radeon HD 7970. That's pretty ancient in tech terms, especially now that NVIDIA is moving away from Kepler. It's three generations old, they should have moved on to Fiji-based chips a year ago.
