Do you think Flash and Silverlight are any different? I'm still yet to even see anyone deploy Silverlight in a meaningful way outside of Microsoft and a very niche Microsoft-loving sites.
I think Silverlight has as much of a right to exist as Flash but honestly we should expect better than to have browsers needing third party plugins in order to deliver animation, video, webcams, and sounds.
For every function you add to the browser, there'll be one more left out. Speech recognition. Touch sensitivity. Full 3D acceleration. Natal like controls.