You are quite correct Pull up. I have a mate who is a tradie in the mines on around $130,000/ yr. Sounds good but once you do the sums it is an hourly rate of about $30. No better if as good as in any capital city job.
What pulls the wage up ofcourse is the penalty rates for the 12hr shifts and weekend work. eg after 8 hrs it is time and a half for the next 2 hours then double time. Saturdays are time and a half for the first 2 hrs then double time thereafter. Sundays double time all day etc. Public hols 2.5 times etc. That is why the mining companies have rolled it up into a salary as it saves them money.
Anyone could earn that kind of money if they do those hours. The problem ofcourse is that usually you have to go to out of the way places like the mines to get the opportuinty to get that amount of overtime,due to the skill/labour shortage out there.
Add in the top tax rate and lack of family time (if your married) and you wonder if it is really worth doing.