"And even if you have an existing traditional Windows app, if you have to rewrite it, are you really going to choose the Windows platform? Probably not. You'd just go with Apple or Android."

Um, why? If you're rewriting it, why would you choose the others? Android tablet sales haven't exactly taken off, and simply starting over on iOS isn't necessarily easy or cheap if you're used to Windows. If you're rebuilding it for Windows 8, both tablet and desktop users benefit.