<Removed Longer Version of Post>
Through using Windows 8, I have determined that the desktop in Windows 8 is not an app, nor does it resemble a Metro-style app once it is used. The Start Screen is part of the Explorer shell, and Metro-style applications running in WinRT can run even when Windows
Explorer is closed. Based on this, it makes sense that WinRT Metro-style apps might be able to run in a window on the desktop (since the desktop still seems to provide the base for the Windows 8 experience).