Not true. The hardware/software discussion is the largest part of the equation.
Apple locks their users into specific hardware for use with their software. Their software works exceptionally well, because it is designed to function flawlessly on the hardware on which it ships. For instance, you can’t install iOS on an ASUS motherboard with nVIDIA graphics cards and expect the same performance or stability as with what they ship it now.
On the other side of the coin, Microsoft tries to be everything to everyone, and as a result, you have a security-hole-ridden, bloated set of software that’s expected to run on a dishwasher if you have enough disk space. Then when you want support for a fault, failure, or operating SNAFU, you spend hours or even days finding answers on the web, installing software, scanning, snooping, monitoring, and even if you find the problem, you often create new ones down the line.
Then you’ve got the middle ground with Linux. Linux can be installed on almost anything from a LiveCD (or USB disk), and generally only the necessary drivers, firmware, and software are installed based on the preferences of the user. There is, however, much less professional, paid support, and unless you’re doing the basic web, email, videos, pictures, and music thing, you’re likely going to spend a lot of time in a bash CLI.
I understand controlling interests for corporations, and I don’t fault Apple for their decision to do what they did. I do not believe, however, that they’re going to overtake Google in something that they’ve already perfected over the course of the last 10 years. Just like with YouTube, people are going to flock back to what they know if it’s taken away from them but still left out there as an option.
It’s more about market dominance. A temporary advantage in hardware or software can be very important to winning a battle in the overall war. If you can hem your opponent in to a small slice of the market even the best platform goes obsolete very quickly.
Do you actually own any Apple product?
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.