Qantas advertise it on their site:
http://www.qantas.com.au/info/flying/beforeYouTravel/travelDocuments
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Forms of Identification
<snip>
If you are travelling domestically and departing from an international terminal (flights QF001-QF399 and Australian Airlines flights), and are 18 years of age or over, you will need to produce photographic identification as below that includes your full name. Your boarding pass will have a special 'D' (Domestic) sticker. You will need to sign your name in the space provided and may also be required to record details of your photographic identication. Retain your boarding pass as you will need to present it at immigration and customs clearance points at the end of your journey. This is required to comply with the Migration regulations administered by the Department of Immigration and Multicultural and Indigenous Affairs (DIMIA).
Photographic Identification
The following are the only acceptable forms of photographic identification all of which must be valid at the time of travel
* National passport
* Motor vehicle driver's licence issued under a law of the Commonwealth of Australia, or of an Australian State or Territory
* A document that identifies you issued by:
- the Commonwealth of Australia, or
- an Australian State or Territory, or
- by an authority of the Commonwealth of Australia, or an Australian State or Territory
* Aviation security identification card issued by the operator of the aircraft or the operator of an airport in Australia
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Seeing it is a Qantas policy backed up by DIMIA policies (which I can't find right now), the Check in agents should follow it.
I could have great fun with this ruling. Will have to try it next time I'm flying Domestic on an International flight and make sure I have a print out of the page to assist if I have issues....