As far as I know they don't have any special deals. They use the open graph "watch" action, and when you install the app you give it permission to post this action (it is the publish_actions permission). What you are seeing on the feed are aggregations of that action. They also show up in the ticker.

As an aside, I do know that Pinterest is allowed to do somethings that other apps are not. I've heard that there are some feature whitelists, and it looks like Pinterest was whitelisted for at least one of them (the ability to send a message to more than one recipient).