Lack of cross-platform support in Silverlight 4 explained
As with any new release, in Silverlight 4, Microsoft has made some changes that developers like and others do not. There are too many to list of the former, and just a handful of the latter, but one of them is quite serious: cross-platform support has become less of a priority
via arstechnica.com
Does anyone really want COM-like support on Mac or Linux?
The HTML control is a problem. I think the only way to fix it is to have a HTML rendering engine built on the CLR. Actually, I wish they'd do this anyways. I really don't like using MSHTML in .NET
