Windows 8 looks like it is a crux were Windows desktop application developers no longer have an exclusive desktop/web differentiation. The boundaries are now blurred. With Windows 8 users will now come to expect a 'Metro' style look and feel meaning that WPF/Winform developers will either need to roll the own or move towards WinRT.
Perhaps it has never been about technology but about look and feel?
I like the idea of a technology change driven by user demand for look and feel. It does not feel as fundamental as the DOS/Windows crux of the late 80s but it does look like a tsunami.