@Paul:do you even know what is Silverlight and WPF ? no you dont.
in my opinion , HTML5 is a mistake. the W3C should have fixed some issues with their previous standards before thinking about HTML5.
Now there is a huge problem with silverlight in my opinion. There are too much differences between silverlight and WPF.furthermore XAML is too complicated for a client developper , compared to MXML and Flash. But the solution is not to make Silverlight a subset. the solution would have been better if silverlight was a framework on top WPF, so you can limit yourself to silverlight for rapid web dev or go down to a more complicated level if you want to go further.