But what exactly can they do on Windows that they couldn't figure out in something like ElementaryOS? Get infected with malware? I think most people are actually pretty clueless about how to use Windows effectively, especially now that we are deep into the Windows 8 world.
MS Office is a big one, Excel is pretty much un-rivalved when it comes to the spreadsheet game. Open/Libre Office are nice but not as good as MS Office, plus everyone already knows how to use it so businesses don't have to spend money retraining them on it.
Don't get me wrong I use OS X/Ubuntu daily and die when I have to use Windows with it's lack of POSIX compliance and abomination of a shell but that doesn't mean it's the right choice for the masses.
Okay, but Office is not Windows. It runs on Macs, and there are plenty of virtualization options for businesses to run Office for people without a Windows desktop. RHEL 7 in particular is built for it. And Microsoft's web apps are getting better all the time. I wouldn't he surprised if the web app catches up to the desktop app in the near future. And everyone's grandma does not know how to use Excel.