The best example I know is politics - so many partisan sites exist that individuals who are firmly within one camp can get all of their news through their preferred filter - unlike MSM which at least pretends to be objective and achieves somewhat middle ground.
For HN, I think it's fair to say there are some characteristics we have in common which are not common in the wider community (say, respect for rationality and intelligence). I hope we're not too insular to only find news and conversation here; if we're are insular, we may wake up one day to discover our values have been even more marginalised in the wider community and we didn't even see it coming.