Ask HN: How do some posts on HN only show the posted time?

Typically HN posts have the following info in small type below the post title: # points, username of author, time elapsed since submitting, flag this post, # comments.

Then there's these that I see once in a while that only show the time elapsed since the story was submitted.

A screenshot of what I'm talking about: http://imgur.com/qWD71