Let me see if I can make sense of this...
If you want to build a Windows 8 application, you need to target the WinRT runtime or no runtime at all. Targeting WinRT will of course give you access to the platform features, where targeting no runtime at all will not (basically you would create an application that can run on its own but not do anything really interesting). So, in the interest of keeping this conversation topical, let's consider a Windows 8 application an application that target Windows 8 features, hence WinRT.
Same thing for Windows 8. Even if you use JS/HTML/CSS, it doesn't mean that your app will run in any browser. Unless it's a very trivial app, it will use *something* from the underlying platform and will, by this, be platform dependent.
So, making the "web way" a first citizen in the Windows 8 app model is not the same as saying that a Windows 8 app developed in this manner will be usable (or even meaningful) in an arbitrary browser. Even using prefectly standard JS/HTML/CSS, if an app targets WinRT, it is a Windows 8 app.