I think people would take issue with the more explicit forms of function annotation being the __only__ option, for the simple reason that they're a bit verbose and ugly. It's very nice for people to be able to just write code that appears to magically work, without any extra noise.
That said, the dependency injection system in angular.dart is a bit different, and we'll likely be learning and porting some of that back into AngularJS 2.0 over the coming months.