I think you may be generalizing from your experience. Just looking at some of the openings for these companies they are looking for MongoDB, HTML5, Rails, etc. I didn't see any mention C# or other MS specific things.
Mainly, I was wondering if there is any sort of outreach by MS to any of these small companies. I know they have a presence in the Valley and have MS Ventures to nurture fledgling companies with start-up capital, but as far as strategizing to keep new companies in their ecosystem long-term, I was curious to see what sort of efforts they are putting forth to address this.