I don't think Google or any other search engine cares what happens once you click a result link. Their job is done once they give you those results.
You have a long way to go in your understanding of how Google works. I'm trying to pass along some knowledge to you, not quibble with you. So please don't take this as criticism of you.
A great deal of Panda is about user engagement with the sites after the click from the SERPs. They engaged quality raters to hand review websites in order to create an alogrithmic rating system for judging things that please or displease Google users about a site. User engagement on the sites they send people is very important. Heck, just today there's an article in the NYTimes [nytimes.com] about how Google is measuring how fast a website downloads. We all know that site speed is a part of the algorithm [mattcutts.com].
The quality of the user experience once a user clicks a serp is paramount to Google. Many years ago I had lunch at the Yahoo cafeteria with Tim Mayer and Jeremy Zawodny. In conversation I suggested to Jeremy Zawodny that something Yahoo should work on is identifying hacked sites so as not to send their users there. Jeremy Zawodny literally rolled his eyes and replied that people's problems with their servers and site technologies was not Yahoo's problem, totally missing the point that the user's experience is Yahoo's problem. About six months to a year later Google started highlighing sites in their SERPs that were infected with viruses, warning their user's about the dangers of visiting that site.
You see, that's another example of how Google is focused on the user experience once they click off the SERPs.
The reason publishers are demoted is by not following policies.
That's just one reason publishers are demoted. The Panda thing is separate from the quality of the content or how the site was promoted. A large part of it is determining if the site looks spammy. That's the big flaw in Panda because it can hit an otherwise non-spammy site just for following Google's own AdSense Ad Placement Suggestions.
[edited by: Robert_Charlton at 2:35 am (utc) on Mar 3, 2012] [edit reason] fixed link [/edit]