What makes you think that? The only thing blocking its legality is gambling, right? Gambling is extremely widespread in Australia whereas my understanding is that there are very few US states where it's legal.
Widespread maybe, but highly regulated, for online gambling like this you need a licence and to follow a large amount of guidelines (anti money laundering etc.)
So, no, I would say this is illegal under AU law
Source: I used to work for an online gambling site in AU