WinRT is technically the API for "Windows Store" apps. Not to be confused with Windows RT which is the ARM version of the OS.
This isn't true, XNA is not supported by "Windows Store" apps or even in Windows Phone 8 apps (it does support them in a backward compatibility mode though)
Didn't say it was xna. i said it is exactly like xna. It like using .net there is not much difference in the rt runtime.