It is very interesting, how the legislation varies from state to state. The main act that covers agency, has the biggest variations. In Vic, if my memory serves me correctly, the agents can take their commission from the deposit in the trust account, when the contract becomes unconditional. That is why they go for the bigger deposits. Under basic "law of contract" no deposit is necessary, however as a seller, I am not sure I would accept an offer that has no deposit, or a minor one. If the buyer does not proceed, all I am left with is litigation, and that is expensive, and uncertain. The other piece of legislation that impacts, is the "Land Sales Act", which I think is a bit more similar, as it come from our Westminister ancestory. That is where the problem of greater than 10% deposit comes in.
So, back to the original poster, I would think in Victoria when the agent gets commission earlier, a higher deposit may make you offer get stronger legs.
regards
Peter Weiss