Clrokr at SurfSec explains how Windows RT's code integrity mechanism can be bypassed to run own-made ARM-based desktop programs on Windows RT, and not just Microsoft's own software like explorer, Office and Internet Explorer. The discovery confirms that the decision to ban traditional desktop programs from Windows RT was a pure marketing choice.
Windows RT is a clean port of Windows 8. They are the same thing and MSFT enforces Code Integrity to artificially separate these platforms. It does not stop pirates from modifying store apps (and their license checks) because store apps are the only things that can actually run unsigned. The fact that this method works on Windows 8 as well shows how similar the systems are. You can even enforce Code Integrity on Windows 8 to see what Windows RT feels like!
The decision to ban traditional desktop applications was not a technical one, but a bad marketing decision. Windows RT needs the Win32 ecosystem to strengthen its position as a productivity tool. There are enough “consumption” tablets already.