In other words, no matter how easy they would be to port, you couldn't make versions of Skyrim, Borderlands 2, XCOM: Enemy Unknown, or Resident Evil 6 to run on Windows RT, simply because Microsoft will not allow you to sell them to Windows RT users. All those titles have content ratings higher than MS will allow for distribution through the App Store.
Ruling out AAA titles feels like a pretty severe blow to any ambitions WinRT might have to be a gamer's OS. Which isn't to say they won't sell games for it; just that it won't be games driving the sales of WinRT devices.