Microsoft wants everything to be on .NET. HTML5 doesn't further that goal any more than Flash does.
Silverlight allows .Net developers to target a Rich web interface from Visual Studio. If you program in windows, you'll naturally choose Silverlight. If you want to develop using open standards, you'll choose html 5. Flash will be gone.
Okay, so maybe don't fuck silverlight and give us <video> to attack flash from both ends? And a pony?
Why do you assume programming in windows == microsoft affinity. Im a windows man and am openly anti silverlight. I am actually amazed its survived this long...