Some use cases don`t allow to use Flash into it`s ordinary fields. Such cases are online games with iOS ambitions or some other projects that need HTML5. Also there are a lot of Flash developers with game dev skills and ActionScript knowledge.
At the crossroad of HTML / CSS progress and understanding of beautiful Flash objective model FlashJS was born. It`s library that allows to develop HTML5 applications in the way that is similar to usual AS3 development.