CIVIL AVIATION REGULATIONS 1988 - REG 166C
Responsibility for broadcasting on VHF radio
(1) If:
(a) an aircraft is operating on the manoeuvring area of, or in the vicinity of, a non-controlled aerodrome; and
(b) the aircraft is carrying a serviceable aircraft VHF radio; and
(c) the pilot in command of the aircraft holds a radiotelephone qualification;
the pilot is responsible for making a broadcast on the VHF frequency in use for the aerodrome in accordance with subregulation (2).
(2) The pilot must make a broadcast that includes the following information whenever it is reasonably necessary to do so to avoid a collision, or the risk of a collision, with another aircraft:
(a) the name of the aerodrome;
(b) the aircraft's type and call sign;
(c) the position of the aircraft and the pilot's intentions.
and:
CIVIL AVIATION REGULATIONS 1988 - REG 243 Listening watch
CIVIL AVIATION REGULATIONS 1988 - REG 243
Listening watch
(1) When an aircraft is equipped with radio apparatus for use during flight, the pilot in command must maintain a listening watch, or must ensure that a listening watch is maintained, at all times commencing immediately prior to the time at which the aircraft commences to move on the manoeuvring area prior to flight and lasting until the aircraft is brought to a stop at the apron or other point of termination of the flight.
Penalty: 25 penalty units.
(2) Where the means of communication between air traffic control and an aircraft under its control is a voice communication channel, the pilot in command and any other pilot for the time being operating the controls of the aircraft shall personally maintain a listening watch on the appropriate radio frequency.
Penalty: 25 penalty units.
(3) An offence against subregulation (1) or (2) is an offence of strict liability.
Note: For strict liability , see section 6.1 of the Criminal Code
This is non regulation designed to absolve CASA and government from any responsibility for safety outcomes.
The kicker is the use of the words "reasonably necessary". Well if you hit anyone with or without a broadcast its the pilots fault. Either you didn't broadcast when you should have, or the other guy didn't listen or one or both of you botched the avoidance manoeuvre. Whoever survives can be prosecuted.
Since you have no way of knowing what is "reasonably necessary" when transiting a CTAF - since no radio noise does ot mean aircraft arent present, the nly solution is to talk loud and long at every CTAF border.