Why does HTML5 not share the same regions as Silverlight?

I have been trying to recreate a Silverlight viewer in HTML5 with all of the functionality that was built in to the Silverlight viewer, unfortunately I haven't been able to find anything that can help me find the answers I'm looking for.  All of the useful regions within my Silverlight viewer aren't present in the HTML5 along with a lot of the individual tools. Any help with this would be much appreciated. :)