Microsoft knows this. I won't be surprised if they have more nd more support for legacy API and applications on ARM over time.
http://www.infoworld.com/t/microsoft-windows/will-windows-8-...
Steve Sinofsky: "We've been very clear since the very first CES demos and forward that the ARM product won't run any X86 applications. We've done a bunch of work to enable that -- enable a great experience there, particularly around devices and device drivers... [W]hat we announced yesterday for the first time was that when you write a Metro style application, all the tools are there to enable you in any of the languages that we support to automatically support ARM or X86. I think that's the key part of everything that we'll run."
Why does the argument that by some magic you'll be able to purchase an iPad-like Windows 8 tablet and run full blown desktop Microsoft Office keep cropping up?
There will probably be a version of MS Works that is written for the Metro touch interface that will work on ARM, but the performance of an x86 desktop application running in an emulator on ARM would be atrocious and everybody knows it.
Why does the argument that by some magic you'll be able to purchase an iPad-like Windows 8 tablet and run full blown desktop Microsoft Office keep cropping up?
Because people like Office, MS makes a lot of money from Office, and MS actually showed full-blown desktop Office running on ARM a few months ago.