I think they probably just don't want to commit to an API for desktop development on ARM yet, because they haven't figured out what it should be. They're trying

I think they probably just don't want to commit to an API for desktop development on ARM yet, because they haven't figured out what it should be. They're trying to make Explorer, Office etc. good citizens in terms of power usage, etc., but are probably doing so in a very ad hoc manner that's not ready to be packaged up for third-party developers (and kept compatible long-term).