[novum]

Facebook calculates an "edge rank" for each piece of content based on metrics such as likes, comments, post time, content type, and so on. Edge rank is used, among other things, to determine the likelihood of a given piece of content appearing in your feed.

Only a fraction of a page's fans will see each update from that page. By some estimates, that number is only 5-10% of a page's fans. So they've earned 700 new fans, but that doesn't mean 700 impressions each time they post.