The night shift story is part of the same basic pattern: women are less willing or able than men to put in hours at work that are incompatible with family life. Working 60 hours a week to get ahead is very difficult for mothers, and so is working the night shift. The nub of the issue is that we live in a society where men often feel comfortable, or at least justified, working those sorts of hours even if they're parents, while women don't.
Chait is spot-on in identifying the strong social pressures that push mothers to choose jobs with shorter or more convenient hours -- jobs that tend to pay less. But what about non-mothers? They face a wage gap, too. Women may want to work longer hours -- pick up an extra shift, stay late several nights a week to make partner -- but are still perceived as unwilling or unable to do so.
In other words, women workers aren't the only ones who are affected by social conventions about how career-oriented they should be. Their supervisors and co-workers are, too -- which can lead them to deny qualified women the promotions or extra shifts they seek. It's not all about women's choices. Gender discrimination still fits into this equation.