Were this a market and were the government enforcing similar, or were this an industry and a regulator enforcing similar, or were this the internet and an ISP enforcing similar, I'd complain as you are. But this is Facebook's platform. Yes, it's unnecessarily grasping, or so one would think if Facebook are really as profitable as they're telling us. Yes, this will panic the stock monkeys. But this is not an entire market, this is not an entire industry, this is not an entire content platform, this is one service.
Besides, perhaps this will even out competition with the minor developer exodus it'll probably end up causing.