Well there does seem to be quite a debate raging on this topic. For instance see this
I’ve always thought that html and the web platform was always playing catch up. From the horror of the reams of script and code that we had to endure in the past, we seem to be getting some form with MVC in asp.net and better UI capability with HTML5/AJAX/Jquery etc
But I’ve always prefered the more natural programming style of Silverlight. And why should the user miss out on the experience just because they are in the depths of the Internet. Sure html5 is great but is it productive? Can it give the ultimate experience? Will all the browsers support it properly in a standard way (repeat html 4)?
In my mind it will always be trying to catch up – pushing the envelope of a space it wasn’t intended for.
However there is still a place for HTML5. i.e. in document driven sites, mobility
But to dismiss Silverlight is folly and depriving your users of the best possible experience they can get on the web.
For me I’m happy to give the user of my apps the best experience in the least amount of time.