Visual Studio 2013 and Blend-for-VS2013 requires Windows 8.1 to use the "Windows Store App" components (both the XAML and HTML Windows Store areas). Visual Studio 2012 is for Windows 8.0.
You must upgrade to Windows 8.1 or downgrade to Visual Studio 2012.
Blend's HTML design tools are only for WWA (Windows Web Applications, aka "HTML Windows Store Apps") and do not officially work for website projects (which is a shame, imoh).
Disclaimer: I'm a developer at MSFT who worked on Blend.