The ACA merely license the frequencies used to ASA.
The licence states, in effect, that communications must be carried out in accordance with the CARs.
The licence (or the Act) does not give the ACA any powers to determine what ATC or pilots say as long as that communications are in accordance with the CARs (and associated regulations). Essentially that is the business of AsA and CASA.
How do I know. I have just ammended the licence (now guess where I work
).
AK