This is for good reason, the courts in the US have a financial incentive to favor them because of the Child Support Performance and Incentive Act of 1998. The states get from the federal government about 10% of whatever they collect in child support, and because men generally make more than women for a variety of reasons, women usually end up getting the children so the state makes more money. Even if custody of the child is shared equally and hence both parties have equal expenses, courts will often order child support simply because it makes them/the state money from federal kickbacks.

http://www.answerisland.com/child-support-kickbacks.html