Well said. I share your suspicions about 40 turning out to be the magic number. I also notice that these articles never seem to allow for differences between people, which flies in the face of my 25 years of experience. I've always felt most comfortable working seven days a week, at a manageable pace each day. Other people need those weekends, and are happy to put in long hours in the week. One of the most productive people I ever worked with seemed to work literally all the time.

As for whether or not it's "exploitive", I'm sure it is, under some circumstances. Some poor dev, trapped by an H1-B, getting ground up with hours upon hours of billable work, for example. But a lot of us are paid through equity. In such a case it's perfectly reasonable to sacrifice for the good of the company in which you have a stake.