The article especially states that this was not the reason women were 'paid less'.

"When scientists judged the female applicants more harshly, they did not use sexist reasoning to do so. Instead, they drew upon ostensibly sound reasons to justify why they would not want to hire her: she is not competent enough."

Pregnancy was not used as an excuse. The other important thing to understand is why people pay so much attention to pregnancy but not to increased chances of having a heart attack or increased chances of alcoholism and drug addiction in men. Why are you going to choose only one difference between the sexes?