Why does an increase in the number of jobs in the USA make make the Australian dollar, oil, iron, gas, gold, copper devalue?
This is an example of correlation rather than causation.
The root cause here is not employment. It's the strengthening US economy.
A stronger economy provides employment opportunities, so unemployment decreases.
The stronger economy has helped strengthen the US dollar because investors are shifting money into the economy. That is not the only reason for the strength of the dollar....the uncertainty in the Eurozone and slowing growth in China are other reasons investors are shifting into the US dollar.
Finally, the USD-AUD exchange rate explains only part of the devaluation of Australian resources. Another driver is the weakening of global resources demand caused by softer Asian and European economies. Even US economic growth has been revised downward recently, and resource prices tend to discount forward looking prospects.
When you look at many things in economics it is worth noting that everything is relative. $1 is only worth what it can purchase. The decisions you make are made in the contexts of your next best option (opportunity cost). In this case, the Australian dollar isn't worth any less domestically. The US has just gotten stronger. With the US outlook being quite positive at the moment, its assets and investments are looking more attractive, thus the appreciation of the USD wrt to the AUD (and many other currencies).