Whilst I cannot say I am a

Whilst I cannot say I am a fan of the HTML5/JS programming combo, I do believe it lends a degree to the ease of use for the developer and an aspect of portability to their finished apps; now, with that said, let it be known that the XAML/C# pair are far superior when it comes to programming power and flexibility.  They were designed from white paper to functional language to be the brick and mortar of modern Microsoft platform applications, both hosted and local.  I do suppose HTML5/JS is suitable for simpler tasks and easier to learn; however XAML/C# is probably the winner of the fight for heavy lifting and overall platform superiority.