Thanks for your question.
Actually we discontinued the support for Silverlight 2 ever since Silverlight 3 became official. We had no reason to delay this decision as Microsoft used to send the update to Silverlight 3 directly through Windows updates. Now that the Silverlight 4 is on its way and there will be significant improvements there, our plans are to officially support Silverlight 4 once it becomes official. We are currently working on a brand new Editing engine. More about our plans can be found in our public Roadmap
the Telerik team