Hey, I've got a radical idea
Microsoft already has a Mac BU (business unit) with Mac developers. Why don't they leverage this available wealth of talent to port Silverlight fully to MacOS X (and by extension, making it essentailly iPhone-ready)?
That would deny anyone the opportunity to say it's essentially Windows-only as a reason for not adopting it? (Moonlight exists for Linux but its feature set lags and is not as compatible or fully implemented as the Windows Silverlight is. My colleagues discovered this the hard way.)
Personally, I think some healthy (true) multi-platform competition is good. I'm not that fond of Microsoft, but they already have this talent in-house -- why not make use of it? Silly, radical idea, I know... :-)