Question: I am having trouble finding a clear answer on this one. I have an ASP.NET 4.0 Silverlight app, but recently a ton of users are complaining about not being able to use the site on mobile devices and Linux distro's. The app is built on MVVM architecture, and thus we are considering changing the UI to alleviate the complaints. We are leaning toward HTML5, but I'm not sure if this is even technically possible with ASP.NET 4.0. I've seen some posts saying that HTML5 only works with javascript code behinds, and that with ASP.NET 4.5 HTML5 support will be added. Am I understanding this correctly? Maybe it would make more sense to just go with an ASPX UI, what are the advantages of HTML5 over .ASPX? Any help is appreciated.

Answer: 
HTML5 is a set of client-side technologies.  

ASP.Net is a server-side technology.  

They have nothing to do with each-other.

However, it will be easier in ASP.Net MVC.
It is not technically possible with ASP.NET 4.0. ASP.NET certainly needs the upgrade in order to handle any HTML5-producing code behind or 'plug-ins.' I second the notion of ASP.NET MVC. Also it seems you are comparing a car to gasoline when you ask the advantages of HTML5 over ASPX.