I have a confusion regarding Windows Store/Windows 8 app development. When creating a Windows Store app in Visual Studio 2012 and publishing it using Windows Store, what are the devices this app will be available at?
Will a single app be available on all mobile, tablets, and desktops? Or versions will be required to created separately like in iPhone/iPad scenario?
For most apps, the app will be available on any device running Windows 8. The actual hardware form factor does not matter.
Now, if you leverage APIs that are unique to a particular CPU architecture (ARM vs. x86/x64, for example) then you will need to target each architecture separately. A typical example would be if you are using SQLLite in your application. The SQLLite binary is different on each platform, so you would need to do separate builds of the application, each targeting the appropriate architecture. Thus, it is possible to build an app that only runs on x86/x64 and not ARM, for example. Again, the form factor does not matter.
UPDATE: Missed it the first time, but WP8 is a separate platform. You can share code using things like Portable Class Libraries between Win8 and WP8, but they are separate Stores, separate projects, separate builds.