Agree, but with a disclaimer: I have a feeling the biggest part of Windows' marketshare 20 years from now will be Windows Server Core instances (running on Azure and elsewhere), with "Windows as PC software" no longer contributing much-at-all to the bottom line, and possibly made entirely free. Business workstations (everything currently running Windows Enterprise) will run something-or-other-that-doesn't-matter that can run Microsoft Remote Desktop, and apps will mostly be delivered via RemoteApp connections to said Windows Server Core clusters.
Microsoft is becoming a cloud company, and enterprises are finally starting to accept thin clients (because now thin clients are actually kind of fat, and thus much less annoying to use.) Windows-on-the-desktop will basically be in a race against ChromeOS, which is fundamentally a thin-client OS as well.
(Meanwhile, OSX will probably... continue to just be OSX. Unless Apple has some big new shift in vision, they're nowhere near being a cloud company, and OSX is nowhere near being a thin-client OS.)