Earlier quoted context omitted.
It all depends on whether it's a job board that hackers will find useful and not something like Monster.com. If it's sufficiently relevant and useful to thread readers, it should be posted. Don't be pedantic, don't make up rules.
Pedantic might be a little harsh, but I see your point. You have no idea how spammy job board people (yes, I'm part of this crowd) can get when they find a new field to peddle their wares. We're just shameless. And if there's isn't some throttle/downvoting, these threads will become 90% "check out my job board" and 10% real jobs.
To argue that HN'rs are incapable of distinguishing between job boards that they personally find useful from ones they don't seems a weak argument.