
Real Applications Don't Run Everywhere
The thought that an app could be written to run on *any* Windows device is ludicrous.
It applies to pithy samples shown in Visual Studio demonstrations and really rubbish apps that want to be everywhere and don't work properly anywhere. For real applications, the entire U.I., at the very least, will have to be entirely redone.
You simply can't design an app for a phone and expect it to be useful on a desktop or vice versa.