I doubt it...Microsoft has a vested interest in steering companies towards higher quality video than FLV can do, there is no money in Silverlight, only in servers...
At one point Real had 80% of the streaming market and look what's happened to them...having 75% of the content doesn't mean they should include it, but I understand why you think they should. As far as CPU load, its an issue but some of that issue has to do with the codec and some has to do with the quality of what is being transmitted...I don't know where the CPU load issue really is...my crappy phone can show VC-1 pretty easily...
(If this has answered your question, please "Mark as Answer")
Shawn Wildermuth
C# MVP, MCSD, Speaker and Author
Silverlight 2 Workshop
May 12-14, 2008 - Atlanta, GA
May 28-30, 2008 - San Francisco, CA
http://www.silverlight-tour.com