I would be surprised if there wasn't an overlap between HN and 4chan (same as with SA). Being run in diametrically opposed way it fills its role rather well, I think. There is no reputation system, no limits, no censorship, etc.. This means it produces many utterly vile posts - but all of them are true expressions of people as they are, not as they pretend to be. I think people often don't appreciate this. It's not just people being dicks on the Internet, it's people saying what they think with no regard to social acceptance or basic politeness. And since there are no credentials, your posts are just that - some text and images conveying ideas. The only authority comes from the content.
Here's to another billion.