In an earnings call recently, Sinofsky stated that Windows 8 devices powered by ARM processors would only run Metro style apps. They will not have support for Win32 apps.
Windows 8 On Arm Will Only Support Metro Apps
Contrary to what most people assumed, it turns out that Windows 8 will be supporting only Metro apps when a device is running on ARM processors. When it comes to the technological challenge of running Win32 apps on ARM, it makes sense that Microsoft would not want to complicate matters that way. In addition to that, ARM devices are generally underpowered as compared to the processing power required to run most full-fledged Win32 apps like Photoshop.
In that light, Microsoft’s move makes sense. Also, Win32 is a heavily x86 focused platform. And now it is fast moving towards becoming legacy. ARM loaded Windows 8 devices are very likely to be non-primary devices. Hence, adding extra man-hours and development to support a legacy on non-primary devices would not make sense when already there’s a lot to be done.
Desktop & Metro Will Co-Exist Only On x86
It looks like Microsoft has made a clear distinction between ARM and x86. Knowing full well that x86 is made for processing power and ARM is good at mobile and power-efficiency, Microsoft seems to have decided to leverage the strengths of both and underplay their weaknesses.
Hence ARM devices wont be forced to the heavy Desktop side of Windows 8. It also makes development of Windows 8 on ARM easier because it will be an upgrade to Windows 7. This would increase the efficiency and the timeline of the development work and hence the end product should be much better.
Over all, even though some people are upset with this news, at the end it seems like a good step forward; one that will ensure a stable product on release.