There is so much more you can do with Silverlight/Flash than you can with HTML 5. I'm not even sure why they're mentioned together.
WPF being dead...I can kind of believe it. It's been around for almost 4 years now and it still hasn't really taken off. I like it, and it makes drastically changing the look of standard controls extremely easy, but for most developers that's not enough
of a reason to move away from WinForms.
I'm probably not your typical "Microsoft-ecosystem developer" but I think the reasons I don't use WPF are the same reasons few other developers use it too:
First and foremost: the WPF designer in VS sucks. You have to use Expression Blend, but that's a separate product with its own learning curve. WPF is hardly as simple as WinForms in getting something up-and-running.
I'm also put off by the lack of WPF applications that aren't ugly. WinForms makes it easy to make something that looks presentable. Pretty much all the WPF apps I've seen in the wild (with the exception of Expression and VS2010) are horrible abominations.
Developers are not designers.
Other things, like the extra initialization delay put me off.