The Aboriginals that live in the outback have a lot of autonomy, basically they have tribal law. The perception seems to be that some of the tribal Aborigines have sort of pushed the boundaries of this - so you have some Aborigines who are good mates with the tribal elders who go relatively unpunished (there was a case recently where a 50 year old guy raped his 12 year old niece and was pretty much let off under the tribal law).

Alcohol isn't part of traditional tribal culture, so it probably doesn't help things. For historical reasons Aborigines see it as part of being granted freedom/citizenship to be allowed to drink (when they were considered Australian fauna they weren't allowed to drink alcohol, as soon as they were made Australian citizens they were allowed to drink). So they drink heavily and get blind drunk and probably don't have a lot of social controls or boundaries on that.

I'd say that a few have done these bad things and got away with it, so the behaviours have become sort of normalised...