Ask HN: Which companies are using .NET?

Most big companies uses it for their internal applications. Most of them contract external consultant or companies to develop and maintain these applications. So thousands of consultancies also uses it. These consultancies also integrate a lot of 3rd party commercial components. The component development companies that develops components also uses .net.

How many startups that uses it? Probably not as many as there ought to be and definitely not enough if you ask Microsoft.

Yes it is an historical HN bias. It has improved over the years as HN has broadened its user base and YC has "followed the money." But HN is still driven by the Silicon Valley bubble and Microsoft's unforgivable sin will always be it's not a Silicon Valley company and did not make the usual lot of VC's rich (it made it's employees rich instead).