I don't think they care. Twitter has reached such mainstream exposure even if every person in the tech world leaves them they have enough clout to remain relevant because large news organisations use it as does the general population.
What pisses me off is that twitter did have the opportunity to be an agent for change such as in the Arab spring. Im sure they could have made up revenue by charging for their API rather then cutting it off. Maybe not as much through controlling the entire ecosystem but at least they would have had a higher purpose then turning a huge profit (perhaps they could have just enough to keep the lights on?).
App.net can never become this change agent as they will be too expensive for most in developing countries to use.