It's not as bad as you say, exactly. Yes, some trendy languages are overrepresented (coughRustcough), and there are people with blinders on about what programming outside the Valley is like. But there's way too much .NET, Java and such posted for HN to be wholly unaware of trends in the broader industry. Java may see some use in NorCal, but I really doubt C# does anywhere near as much as it pops up here.