[mun2mun]

Why are you thinking from just on page's perspective? Most of the time a page is liked when a friend of the user shares a post from the page that the user finds interesting, it may be a kitten image, funny joke, a post about your favorite movie/actor, or about a good food on a restaurant etc. Number of pages he likes depends on how much he uses Facebook. If he is moderately active the number of pages he likes would certainly reach 3 digit number. Now imagine 15 posts per day from each of the pages! It is definitely annoying. Now you are saying about "Most Popular" setting, on which criteria will you define a post belongs to popular category? Recommendation engine is a hard problem. Page owners may complain that their pages are not getting any traction. So I think it is a fair option to pay a small price to Facebook to make sure that the post of the page will surely reach to its followers.