I don't see why this debate continues to rage on - it has no meaning in the context of reality... It's been made very clear - beginning at BUILD 2011 - that this is not about This vs That. You use what you know how to use, what you want to use, as it relates to HTML5 and Windows XAML for building Windows Store Apps.
Please watch http://channel9.msdn.com/Blogs/Bytes+by+MSDN/Bytes-by-MSDN-Windows-8-Design-Tools and start building apps in HTML or XAML, whichever you prefer!
IMO, it continues on because there's a lack of trust ever since Microsoft curtailed work on WPF/SL. There have been several posts here (and tons elsewhere) where developers are looking for something concrete to hang their hat on. Unfortunately the days of a nice homogeneous environment provided by Microsoft are over and we just have to get used to the fact that we'll be writing apps on a variety of platforms with a variety of languages and APIs. It's browser compatibility 10x now that devices are in the mix and web apps are "all the rage" with HTML5 and all. The dominance of the PC is over and that's too bad. Web sites, mobile web apps, native mobile apps, native W8 apps, desktop apps, and on and on; it's a headache, costs more for everyone, etc. but it's the new reality that we live in -- and IMO thanks in large part to Microsoft's decisions these last 3 or 4 years.