Yeah but how much of your population would fall under "tradesperson or builder". Usually the size of your that in relation to your population is governed directly by your GDP output. Australia and the US have very comparable GDP output and people that would fall under "tradesperson or builder" here make up well below 1% of the population.
Australia does indeed have an income tax that's progressive, but you also have to look at why games cost as much as they do. Your country is taxing imported goods to promote domestic consumption. When you look back at your labourers making an average of 70k USD then you have your reason why. A very small amount of the population is using their political clout to impose a regressive tax on goods to prop themselves up.
That tax chart is a joke. If you're paying a 30% markup on goods imported into australia, the 0-18,200 range of income is paying a lot more than it would seem. Maybe these are just labeled luxury items and that's why they're being taxed like this but I'm always hesitant when I see industries that make up such a small amount of the workforce have disproportionately higher income than in other countries. There has to be inefficiencies going on.
I wouldn't call qualified builders, laborers. The games are 50% more expensive but the minimum wage is 100% more than United States, so I don't see your point. The OP is just complaining because he is paying what you would in stores, alot of publishers on Steam charge American prices, for example $50USD for XCOM Enemy Unknown, where as in a store it would probably be $90-100AUS.