Seems to me that you are missing the key point.

If FB did not declare itself a platform...if it had not encouraged others to build on its platform...if it had not encouraged DC to build his product on this platform...then you would be right. But if you are a platform, if you do encourage others to build on your platform (which is the whole point) and if you encourage a company to continue developing a product then it is not right. It may be realpolitik. It may be that having done all those things the platform company realizes that something it has encouraged is more strategic than it had realized, that it doesn't want a third party owning that product and it has to reel back its promises (which is what is sounds like here) but that is (a) a crippling result for the poor developer who took you at your word, and (b) and blow to your credibility as a platform. One incident like this won't kill you. Two won't. But at some point people just won't develop on your platform because there's no trust. ALL successful platforms have to walk this tightrope. Some do it better than others.