It depens on what you consider .NET. The CLR? The .NET metadata schema? C#/VB? The only thing that isn't incredibly important in WinRT is the CLR proper. But the other aspects of .NET play a huge role in WinRT. They even went and largely reimplemented the BCL. And the API design guidelines across the board are .NET based. WinRT looks a million times more like .NET than Win32.