But that's more a testament to the vendor's "now with $AWESOME_PLATFORM!"-driven software architecture paradigm than any real fault of Silverlight or Java. (Except that they both appeal to those sorts of people.)
You see it a lot in the enterprise world.
Facebook also has a couple of applets I think.
So what about Silverlight? Silverlight is really a tooling play. And with HTML5 they're beginning to see that they can bring the Silverlight tooling over to HTML5. The big question is probably layout more than anything else.
Silverlight then becomes their platform for future features of HTML. Rather than "embrace, extend", they extend via a plug-in, and then as feature prove useful, they get them through standards (which is common in most standards spaces).
This is really the path that Adobe should have down with Flash, and based on what I've seen with CS5, I suspect it is, they're just getting to it really late.