Band a Lot:
Yes, CASA is responsible for implementing Australia's obligations under the various Annexes of the Chicago Convention. Nevertheless, if a State finds it "impracticable" to comply with ICAO SARPS, it only has to notify a "difference" to ICAO. Without getting into the 121.5 argument, Australia has filed 100s of differences with ICAO - they are published as a supplement to the AIP. The current supplement is available on the Airservices website:
http://www.airservicesaustralia.com/...p/s15-h104.pdf