Because https://www.facebook.com/wikipedia counts as a brand page, this article is kind of interesting for us as well:
http://www.nytimes.com/2014/11/15/technology/facebook-to-cut-unpaid-posts-by... TLDR: starting in January, Facebook will down-rank some posts from brand pages that are considered too promotional. Nothing to worry about too much; it's also not the first such announcement, I recall that one or two years ago there were changes that likewise triggered discussions whether FB was trying to pressure all brands into buying paid ads instead of just putting out normal posts. But it's probably worth looking at the example in the article for a post that is too promotional.
Also interesting are these numbers: "Now, when a brand publishes something to Facebook, 2 to 8 percent of its fans see it, according to outside estimates." This kind of matches the range many of our posts are in, although we also have quite a few way below 2 percent. To wit, the page has 4.2 million Likes right now, and these are the five posts with the highest Reach numbers in the last three months:
Nov 8: Aaron Swartz post recycle - 630.8K Nov 15: King Joffrey - 334.1K Nov 16: Goodall Family/Kiwix - 271K (already) Oct 3: WMF grant for Egyptian Wikipedia's WikiWomen online writing competition - 261.9K Oct 27: NYT article "Wikipedia Emerges as Trusted Internet Source for Ebola Information" - 261.4K (plus 202.4K in a second post for the same link)
As a comparison, the highest Reach (by far) for a single post in the first half of 2014 was the 315.4K for the Eurovision post in May, when we still had less than 2 million Likes.