I'd have to say there is a lot more than location that makes Australians different to Americans (USA), particularly as there are some Australians living in America and visa versa.
Your questions asks the difference between the people, not the country and I'd wager that there isn't a great deal of difference when you compare the norm (household income and median age) though you will find a lot of diversity in individuals.
The biggest differences that I see (and my husband is an American living in Australia) are to do with our choices of Government. We tend to be more socialist with a relatively strong social welfare system including a Medicare system that provides free medical assistance to all Australians. I was actually paid $4000 to have my daughter and it cost me $0 in medical fees and yet I had an emergency C section and was provided with a nurse who visited our house for a week after I was released from hospital.
And it would be remiss of me not to mention being as it is Australia Day (26 January), that our indigenous people are vastly different and the current society which is part of our history is only 223 years old, our constitution which joins New Zealand to us is much younger barely over 100 years old and though many Australians may not like it, we still have a sovereign by hereditary right, Queen Elizabeth. And this provides Australian's with great ties through the Commonwealth of Nations.
Our native accents, our education systems, shoe and clothing sizes are quite different as well and we tend to watch a lot more imported entertainment in the way of TV shows and movies (they are usually from the USA!). Australian's also abolished the death penalty in 1973.
It's really hard to choose which one is the biggest difference but perhaps it is what we call.. Mateship.