"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.
But there won't be desktop Windows 8 ARM users, so you'll have to re-engineer it twice? Unless there's some quick and easy way to write code that compiles to both architectures without fuss. But even then you essentially have to build two UIs.
I wonder to what extent any under-the-covers code is shared between apps that run both on iOS and OS X (like Pages, for instance) and whether there's any economy of coding scale there.
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.