I've been here 6 years, and my observation has been that the startup culture as a whole leans away from MS, if anything. Startups founded by ex-Microsoft employees do seem to be more likely to use Microsoft tech, but certainly not always. But remember that the wider tech scene here is much more than just Microsoft. Amazon is a big force, and Google has a respectable presence too. Also, mobile development is huge here now, and almost all of it is for iPhone or Android.
The great thing about developers is that they love to try new things, so even Microsoft's developers recognize that the Microsoft stack is not the best at everything.
Most of the people I find who have their heads stuck in the Microsoft stack are non-coders, and those are less common at startups.
