Documentation for Miracast in Android seems very lacking. According to Wikipedia, Google decided not to support Miracast on the Chromecast, probably because it

Documentation for Miracast in Android seems very lacking. According to Wikipedia, Google decided not to support Miracast on the Chromecast, probably because it is an open standard that would have made the effect of selling the Chromecast cheaply weaker on their goal of raising Android adoption and locking in customers. I don't think that all commands are relayed over Google, since if that were true, Android should be clever enough find my Chromecast if I was connected to another WiFi network. The delay would also make it impractical for quite a lot of people. IMO chromecast should have been based on open standards. Android Wear would be just be as heavily "reliant" on Google Now as Android is. Google just decided to give it a proprietary version of Android that is heavily integrated with Google Now. Android Wear could do quite a lot without access to Google Services. It is actually pretty pleasant to use without talking to your watch. It seems like we both have different points of view on this, but in my opinion Google has acted in a way that favours their interests over their customers' freedom.