Read the whole thing. His take is reasonable. If Windows 8 does ship with support for classic non-Metro apps on ARM machines, these will be the reasons why.
But there are other good reasons, I think, for why Microsoft should cut the cord cleanly and go Metro-only on ARM.
via Daring Fireball – The Case for Going Metro-Only on ARM. When I posted the link about Windows 8 being able to run normal desktop apps, I somewhat flippantly said that it “could keep Windows 8 from being truly awesome”, this is why.