That's not an entirely fair description. Windows RT is a real Windows 8 installation, but running on ARM, and restricted to running only executables signed by Microsoft.

Windows RT is built from the same source code as Windows 8 and virtually all Windows 8 features are there.

Well, how do you define "Windows"? Windows RT (not WinRT!) is ARM based Windows that can only run "Metro-Style" apps. With the exception of Office that comes preinstalled on Surface RT. It still has some familiar features like the desktop, command prompt, Explorer, like normal Windows OS but you can't install any desktop software.

So it's like using Windows without the benefit of the solitary advantage of actually using Windows.