In an effort to clarify its position and calm developers, Microsoft posted a very well crafted blog post which details its position on the discussion of using Silverlight versus HTML5.
The debate stems from an announcement that Microsoft previously released which said that HTML5 was the way to go, and Silverlight was to be used only on Windows Phone 7. As you can imagine, developers who had spent considerable time and effort to create apps with Silverlight were rightly concerned.
The main focus of Microsoft’s recent blog was that each technology has its uses. Silverlight is useful as a plug-in based experience, and HTML5 is useful for many different scenarios, and developers have the best of both worlds to choose from.