The Linux desktop has no more difficulties than the MS desktop (which is also endless "poor UX, drivers, audio services, file system snafus, [...] upgrades gone wrong, bad advice on forums compounding problems.") With a billion dollar marketing budget (like either MS, Google, or Apple) and/or a hardware manufacturing company behind it, it would sell.

That's not even really a complement to the Linux desktop, it's more a statement about what a billion dollars can do.

The quality of the desktops of the members of this oligopoly has a negligible influence on the uptake IMO. The iPod/iTunes pair was one of the functionally worst (but one of the prettiest) products of its category. Android and iPhone have taken nearly a decade to reinvent basic functionality taken for granted on most computers. Doesn't matter.