Earlier quoted context omitted.
I think you're wrong about the write-once run-anywhere software ecosystem that Windows had to deal with. There was an incredible proliferation of different hardware -- including drivers etc. -- and it was mostly up to Microsoft to make sure that the OS continued to work flawlessly (or at least at whatever level of semi-stability it managed to attain) across all of these different configurations. This is an enormous r…
I think you over estimate the number of types of harware each platform had to deal with. PS: Orders of magnitude 3 = 1,000, 4 = 10,000, 5 = 100,000. Now if you ment 3-5x the number of platforms but 1000x is way to high.
Sure there are standards to describe hardware interactions, but any reasonably experience sysadmin will tell you horror stories of when they found a weird issue with chipset X not following the standard just right, and needing a special case driver that no longer worked with the OS of choice. This means there are combinatorial multipliers on a per device basis (or some percentage thereof...)