I think you're all wrong, nothing to do with Panda or Penguin
Its being going on for more than2 years now
When you add an affiliate section to an info site, or vice versa, both suffer greatly, i wasn't sure till I noted that the really big sites in the sector I am interested in had enforced strict separation of both
To complicate things, it doesn't actually affect the top tier of well know branded sites, for obvious reasons
Document/webpage/website classification anyone ?
Just opinion , probably wrong, but it irks me to see folk labelling web pages inferior , when per the op, they were useful to visitors