Synthetic chemistry was more or less started in the 50s and 60s by a professor at Harvard. He worked his students hard. Therefore when they went out and had their own lab groups they worked their students hard. The process perpetuated itself because that's one way to get breakthroughs and results. Now 50 years later most of the respected synthetic chemistry labs in the country operate on these ridiculous schedules. Now for the gory details. The professor and Nobel laureate, Elias Corey, that started it all has had three suicides in his lab group. (By the way the article linked above is really good and very long.)
My graduate school experience is not nearly as threatening. I suspect that most graduate school students enjoy life as much as they ever have. That 70-90 hours a week attitude is not one which pervades all fields of science graduate life. I encourage people to go to graduate school but before you do make sure that it is the right choice for you.