I had previously pointed out that the lack of supported platforms was a serious problem for Silverlight, especially when compared to Flash. The root of the problem was that Moonlight, the Linux version of Silverlight, is usually at least one release behind the Windows and mac versions of Silverlight. This caused confusion for developers as it was not clear which features would work on Linux. Rather than working to fix the problem it seems that Microsoft is making it worse by introducing Windows only features in Silverlight 4.