@DeathByVisualStudio:

 It's my understanding the W8 apps produced by Microsoft so far are all HTML and they seem to do was well as any WPF app I've used on the desktop.

This isn't quite true ... most of them are HTML but not all. Off the top of my head, Bing Maps, OneNote MX, and I think Fresh Paint are all XAML (+ Direct3D) based.