Metro Style apps can be developed for the following architectures:
Out of the above three, both x86 and x64 architectures support both Metro apps and traditional Windows programs. However, the Windows 8 on ARM will support only Metro Style Apps. The traditional Windows applications will not run on ARM architecture.
If you are looking for true cross-Windows deployment, you may want to choose Metro apps instead of traditional Windows programming.
The best part of Metro Style Apps is, your apps can run on various Windows based devices including desktops, laptops, tablets, ARM devices etc. Deploying same app for various devices will significantly reduce your development time and efforts.