Ah buckshot:
You pose a very intelligent question that is crucial to this Unicom debate because:
1. The US Code of Federal Regulations (Part 87 Subpart G) detail the regulatory requirements for the establishment and operation of Unicom in the US; and guess what?
2. The provision of traffic advisories is not mentioned, or even high on the list of services that Unicom operators are authorised to provide (
eCFR ? Code of Federal Regulations)
So, although it would appear that many Unicom operators in the US are providing traffic advisories on pilot request, the question we should all be trying to find out is whether they are operating legally and what is their (or the airport's) legal liability exposure if something should go wrong?
Also the FAA's Advisory Circular AC90-42F does not list Unicom provision of traffic advisories as being a desired function:
8. INFORMATION PROVIDED BY AERONAUTICAL ADVISORY STATIONS (UNICOM).
UNICOM stations may provide pilots, upon request, with weather information, wind direction, the recommended runway, or other necessary information.
In my view one would be stretching the regulatory interpretation that the provision of traffic advisories by Unicom would fall under the category of
"...other necessary information"
Therefore, any international system that is being considered for potential deployment in Australia must be deployed in compliance with the associated home regulations, not in accordance with someone's perception of what is/is not allowed or happening in a foreign country.
Just because it is happening overseas, doesn't necessarily make it legal or appropriate for the Oz airspace environment.