Well.. everyone thinks "basic desktop user" to mean different things. The problem is I don't think there is such thing as an average user.
Every workplace is domain-specific, and domain specific software is simply a tool to get the job done. Windows/Linux is completely irrelevant and of absolutely zero consequence IMHO. You pick a tool that you know will get the job done, and simply use whatever OS it works on. We use a lot of scientific software at work and a 100% of it requires Windows. Yes, it could easily be re-written to work on Linux or OSX but that is not the case at this moment. If we were an accounting firm, we'd just pick Quicken or Quickbooks or whatever tool people were familiar with and use it. Or if we were an magazine or an architecture firm, or an electrical company, we'd again use whatever tools we need to get the job done. As far as the OS goes, the only thing people care about is whether their tools still work on version N+1.
For various reasons, Linux and OSX require much more involvement from the vendor to keep the software running. OSX is very user-friendly, but very hostile to developers who just want to push code out, and not be shackled with supporting the new flavor of the month API that Apple comes out with.
Windows requires very little time investment from the vendor to make it work on newer versions. Heck we're using Windows XP software (like.. binaries compiled decades ago) on Windows 10 without issue. Yes, obviously, giant caveat here - I'm not saying windows never has API breaking changes .. I'm only saying the probability is much much lower on Windows than any other platform. (discounting esoteric options that nobody is using)
People who are cheer-leading Linux or Windows or w/e, never seem to "get" this. Nobody really cares about the OS.