As a freelancer who has had multiple contacts (and occasionally work) from HN monthly posts, I can say it is not that rare. The people looking for freelancers rarely post, they do apparently look over it to find people to contact, though.
Hm but you are saying the same as me, that "The people looking for freelancers rarely post". I never said they don't look at the freelancers who are looking, I haven't tried it myself so wouldn't know that. It's nice to know that happens though