Bob Muglia, Microsoft's president of tooling and servers, has confirmed
recent rumors that Microsoft is changing the mission of Silverlight as a platform to meet the needs of changing markets. Muglia says that Microsoft is now aiming Silverlight at customers who want premium RIAs and rich media content. For customers that want more cross-platform portability they are going to support HTML5/CSS3/JS technologies, which have the broadest reach.
Silverlight is shifting more focus to the mobile universe. Silverlight constitues one of the main application development platform for Windows Phone 7. The announcement should be welcome news for people who were happy when Silverlight became the platform for WP7 development.
Now Silverlight development could focus more heavily on the mobile development features, so WP7 developers might get a much deeper and broader tool set for developing mobile applications and applications for other form factors such as tablets and set top boxes. However, Microsoft understands that HTML5 is the only fully cross-platform solution, even for Apple's iOS.
The move makes sense for Microsoft, who was beginning to show support for HTML5 by bringing its next browser, IE9, up to compliance with the latest web standards. They are also using HTML5 in their Bing search engine and HTML5 video for live streaming on Xbox 360, instead of using Silverlight Smooth Streaming.