WinCE has a very large subset of desktop Win32 APIs. Of course it's not binary compatible, we're mostly talking about ARM platforms on 'phones.
Linux has the whole apt-get/aptitude/whatever thing but that's not going to be the draw in the mobile space. Something based on it maybe, but it's gonna have to be a whole lot more user friendly to compete with the App Store etc. Even if it's more free(TM)... And of course few people are going to develop for it if there's no return on their investment.
Linux makes a large amount of sense on a nerd targeted netbook, in fact as a mostly Windows user I might switch to something like that, but the mass market is still not driven by the forces you would like.
Some of your points are well made.