Direct quote from the Oz AIP. My bolding.
A traffic information service will be provided, where applicable, depending on higher priority duties of the controller or other limitations; eg radar limitations, volume of traffic, frequency congestion, or controller work load. Radar/non-radar traffic does not relieve pilots of their responsibility to see and avoid other aircraft. Pilots are cautioned that there are many times when the controller is not able to give traffic information concerning all traffic in the aircraft's proximity; in other words, when a pilot requests or is receiving traffic information, he/she should not assume that all traffic will be issued.
Also, Civil Aviation Regulation 163A
Responsibility of flight crew to see and avoid aircraft
When weather conditions permit, the flight crew of an aircraft must, regardless of whether an operation is conducted under the Instrument Flight Rules or the Visual Flight Rules, maintain vigilance so as to see, and avoid, other aircraft.
Visual aquisition of the other aircraft was the last resort available to the prevention of the GOL 1907 accident. It's debatable with the closure speeds in that case (head on) whether avoiding action may have been possible. However, it would be nice to think that crews were not relying solely on TCAS to avoid a thunderclap meeting.