I seem to recall from earlier threads when Chromecast first launched that the data path for dedicated Apps vs casting from a Browser on a PC were different.
As in for netflix, your phone/tablet send a command to netflix's servers and they streamed the content down through the intenet to the Chrome cast device, where as for Tabbed casting, of ESPN for example, your PC sends the request through the browser to ESPN, then ESPN sends the content to your PC, then your PC sends it over to Chroemcas. I'm no expert but if this is what is occuring it become obvious why casting from Chrome may be a litte ways off for moble devices. When it does arrive, These forums will flood with people compalining about the battery drain.