I'm a Silverlight fan and agree with him. The sheer volume of .NET developers alone make Silverlight a highly likely candidate for success.
One thing that he didn't mention and that I think will push Silverlight to mass acceptance is that it will, at some point in the future, be hostable on mobile devices. Silverlight is just a control (or collection of controls) on a web page. The browser, and the Silverilght runtime/VM host the control. So mobile devices only need a host for Silverlight and then Silverlight will become ubiquitous.
Will Moonlight 2.0 be that host for most mobile devices?
Neil McAllister wrote yesterday The case for supporting and using Mono in which he says:
And that's the crux of it.