There are many, many Australians who will intervene if they feel they can stop violence, no matter what country they are in.
I have personal knowledge of an Aussie girl - in her early 20s - who intervened in a late-night rape in the US, scared the rapist away by going out there yelling and making great noise, then took the victim into her own home until the police appeared. (Turns out it was an attempted date rape.)
Yes, the girl could have been hurt or even killed. Fortunately, she wasn't. But she couldn't live with herself if she let the violence continue.
We just have not been conditioned with the same level of fear, and we have been conditioned to help the victim ... personally if we have to. We just don't expect to get killed by the police.