Not entirely true - you might want to look at "Hackintosh" and you will see that there are some clever boot-loaders that do precisely what you are suggesting. There are thousands (if not close to a million) assorted users who are booting into the Apple OSX environment without purchasing a single apple product. However, IMHO you would be best served procuring a Gigabyte motherboard for this exercise, as they seem to work very well without any hiccups at all. For some reason, Gigabyte motherboards "mysteriously" seem to support Apple configurations - and it is quite easy to build a better Mac, than what Apple sells in the Mac Pro market-space (at a fraction of the cost, btw).
Your point with MSFT is quite true, spent years doing regression testing when I worked R&D for both Intel and AMD. Although "Compatible" and "Compliant" may appear to by synonyms - there are subtle differences that make life absolute hell to the motherboard designers. MSFT works on literally tens, if not hundreds of thousands of potential combinations of components, processors, memory, peripherals - that is a HUGE undertaking.
However, the very strengths you list for Linus are equally legitimate with the OSX, as it is based off the Darwin kernel of Unix.
I worked in several design shops and architected numerous hardware solutions in my 20 years in IT, but none of them involved Apple products if for no other reason than the fact that we couldn’t get support for the OS once the system was running.
I wouldn’t use compatible or compliant interchangeably, as in my world, they mean two very different things.
That aside, I want to reiterate that I’m not bashing Apple. I’m simply stating that from a proprietary hardware/software matching standard, they’ve got the market cornered. Yes, while you can install OSX on “third-party” hardware, you make my point for me by showing that Gigabyte “mysteriously” works with their hardware. The point is that Apple only SUPPORTS hardware/software combinations that they design and develop. Like I said initially, you could install Windows 98 on a toaster if you had the motivation and drive to do so.
If you crack open an Apple product, most of the chips and mainboard components are either nebulously numbered or devoid of any manufacturer’s markings unless you know where to look. However, the same dozen or so PCB manufacturers in China make the overwhelming majority of hardware for today’s computing devices, so it stands to reason that there’s always going to be some particular brand that works better than others with Apple or even HP/Dell.