I was thinking the same thing. It's much harder to follow conversations without them.
There was an update to the site today, and they were gone when it came back online.
If you look at the HTML code, they're completely missing:
<a href='http://www.gamedev.net/topic/639919-where-are-the-blue-dots-and-stars/?view=getnewpost' title='Go to first unread post'> </a>
There should be an img tag in the middle of that huge empty a tag!
I'm sure someone will be on the case soon!