I would have thought that the kind of people who post on HN are going to be better at correct use of English than those on your average Facebook/Twitter stream.
Maybe 2-3 years ago, but nowadays Hacker News is just as commonly used as many news services. It's also not only about the correct use of English, many people can use English correctly but do not bother" capitalizing or punctuating since it's "annoying" to do on mobile devices - and since the people who do use Hacker News tend to be more forward-moving with technology, they tend to read and make posts on Hacker News from their phones and mobile devices which they do not bother correcting themselves on.