What makes you think that Microsoft can't have a part of the Unix server slice, either? Have you seen e.g. this:

http://blogs.msdn.com/b/dotnet/archive/2015/02/03/coreclr-is...

(specifically the part that says "We will be adding Linux and Mac implementations of platform-specific components over the next few months.")

Or the part where ASP.NET vNext runs on Mono as the officially supported platform?

http://graemechristie.github.io/graemechristie/blog/2014/05/...