So, because IE supported part of PNG before other browsers, and because JScript was the only ECMAScript compatible implementation a gazillion years ago, it's o.k. for IE to lag behind now?
I'm a fan of certain Microsoft products (C#, .NET, Visual Studio), I like Windows, I see a lot of potential in Silverlight, but I don't see it as a replacement for HTML. Especially considering the fact that Silverlight is not supported in Opera or on any
other platforms than Windows and Mac OS X. Sure, we have Moonlight, but as long as Microsoft remains vague about what its intentions are related to Mono, a lot of people will remain wary.
I'm not saying it is, but from the outside it seems like Microsoft is trying to hold back the de facto standards other browsers are pushing (SVG, canvas, …) because it doesn't match with Microsoft's ideal future (Windows everywhere).
There is the issue of self-canibalization: since Silverlight is now Microsofts pendant to Flash and these media engines support vector graphics, video, animation, etc., it becomes a question of whether to support both fronts equally (Silverlight and the
browser) or let one stay ahead of the other. In a sense, if all browsers started supporting vector graphics and video, that might dampen the evolution of these plugged-in engines.
It's probably fair to say that Microsoft prefers the Silverlight architechture to the W3C jigsaw puzzle, otherwise I'd expect them to fully support SVG, SMIL, etc. There's another reason for this preference and that's the natural glide path from Silverlight
into WPF with Visual Studio and Expression Blend being the premier development tools for these APIs.
On the other hand it's probably also fair to say that a certain lesson has been learned in that it is not wise to lag too far behind other browsers. So there will be some form of co-evolution, probably - with Silverlight being the clear priority...
In fairness, IE supports or supported native vector graphics via VML and? HTML+TIME - although maybe not in the IE8 engine; I heard CSS expressions (I forget the precise name) were also phased out - but they were proprietary anyway.
I see plugins as a playground for new developments that can be rapidly deployed to the Web (depending on the update experience of the particular plugin).