[arnauddri]

I don't think so, it's user-curated. If the job is not interesting, it won't be retweeted so it won't appear at the top of the page, just like HN

[dan_bk]

Who goes on such a site? Jobseekers. Which jobseeker has an incentive to retweet a job s/he finds interesting? Usually YOU want the job you find interesting. Why retweet it when this makes it harder for you to get the job?

[PEntremont]

Jobseekers are not expected to retweet. Company stakeholders and relevant jobseekers friends are.

[webmaven]

And what happens when you add retweeting spambots into the mix?