As a lawyer and a new mother I was doubly offended by this. Most young lawyers don't make a lot of money. The very small percent that do are working 15 hour days and are not thinking about childre because in big firms, when you're a junior baby = career suicide.
Are there women who earn $150,000 who might have a baby? Sure. Some as you say are the main income earners, some might be single, and yes some might have husbands/partners who earn more. But why should we begrudge those women? I would argue that they are the most likely to drop out of the workforce if there are too many barriers in place. Paying them their wage for a few months may make the difference between that woman returning to work, or that woman opting out of the workforce because it's "all too hard". Long term, that is a loss to the economy.
I'm not saying women shouldn't chose to stay home if that's what they actual prefer to do. A lot of times though, it's happening more out of circumstances than actual choice.