It is Chromecast's integration of HDMI protocol extension HDMI-CEC that is responsible for the device's increasing couch-friendliness. This protocol extension is able to pass and receive commands between many of the components typically attached to your TV. For instance, HDMI-CEC is put into play whenever you use your TV remote to cue up and start "Guardians of the Galaxy" in your Blu-ray player, and since its introduction Chromecast has been using it to turn on your TV and to manage input avenues whenever media is pushed to the device.
And in case Chromecast's enabling of your TV remote isn't fun enough, the device sends player state across to your mobile device, too, allowing you to pause playback with one connected device and start up again using your phone, and vice versa.
Google hasn't specifically said it, but there may be a reason the company has added support for standards-compliant television remotes that reaches beyond general coolness. Android TV devices that feature Google Cast are very much in the offing, and it is reasonable to assume that most if not all will include a traditional TV remote control in the box. Thus, to avoid the confusion inherent in supplying a television remote that is unable to start and stop Android TV Google Cast playback, the move to support standards-compliant remotes makes perfect sense.