Planet13 - 1:16 am on May 1, 2011 (gmt 0)
I believe the ads are the #1 factor, however I'd love to see an example where one of the Panda winners was displaying the opposite behavior.
I don't know if this fits exactly with your question, but...
I was searching for something on g (don't remember what it was now), and about.com came up number 1.
Then there was about two paragraphs of text, maybe 70 words total, then a link to page 2.
I didn't go on to page 2, because I saw that the article was going to span 7 more pages, and probably they would all follow the same format.
Of course, about.com has lots of ads surrounding the content - not to mention that popup.
So, either about.com is whitelisted, or google has a more subtle policy than Ads = Bad.