no in australia mate, its law that the biological father must contibute to the upbringing of the children.
I'm divorced and my kids live with their mother in another state. Based on law I have to pay 32% of my pre-tax income to my ex, post tax, either monthly, fortnightly or weekly. That means that I pay my ex an amount not far away from half of what I take home a month.
So in australia, the non custodial biological parent pays through the nose. Btw, I should note that there is no requirement for there to be proof of who the father is, other than the mother claiming who it is.