@netmeg A Forest is made up of trees. To understand the nature of the forest, you must know what kinds of trees are in it.
Panda wants a very specific kind of tree in your forest.
Obviously that one thing is not the magic fix... but it might be a component.
If all the winners have a policy of not linking to competitors, then it could mean that Panda takes into account how much link juice a site has flowing out versus flowing in.
If every article on your site links to someone else, then you have way more link juice going out than a site that does not.