I agree with many of the points brought up. It's strange to me that Facebook would consider a practice that limits the number of eyeballs on their pages. For a social network, the real competitive advantage is the number of users and how engaged they are. While they may make more money in the short term, cutting into the developer ecosystem (healthy as it is now) will cut into their reputation and eventually their bottom line.

On the other hand, I could see them charging just the top 1% of the heaviest API users. In that case, it would fit Michael's cases for when charging for an API is ok.