If Silverlight doesn't get it's act together, that won't be the case for much longer. I've criticized Silverlight for a lack of ambition before, for example HTML 4 is far better for laying out text than anything in Silverlight or WPF. But in HTML5 there
is not only the Canvas element that will let developers do most of the 2d graphical operations they couldn't do in traditional HTML, but it will (most likely) have WebGL which gives web developers a proper immediate-mode 3d API for the first time. Silverlight
could have given that to developers years ago, but right now even Flash 10 has a more powerful 3d facility than SL.
As for the complaint from twitter, Microsoft is a big corporation with multiple divisions. HTML5 is getting a lot of attention with the IE9 team. It's clear that the Windows division hates WPF (and probably .NET in general) and has no intention to ever use
it, hence the development of Direct2d, DirectWrite and that animation thing that nobody is ever going to use because there's no authoring story for it. Meanwhile Silverlight, WPF and .NET in general come from Developer Tools Division (correct me if I'm wrong)
where they still have plenty of support. Basing the Visual Studio 2010 shell and editor on WPF is their attempt to get people to take it seriously, but it's not had much impact so far as I can tell.
"HTML 4 is far better for laying out text than anything in Silverlight or WPF"
One bad e.g., in HTML, if you have a 100x100 div, with a span inside it with a loooong Url as text, the Url/text doesn't break to fit inside the div, it just stays on one long line.