The way I understand it, those 4 hours a day are the minimum required for basic sustenance, anything beyond that you do because you LOVE to do it, not because you take some grim satisfaction in accomplishing something you don't really want to do.
It's great when someone can earn their means to basic sustenance in four hours a day. They can fly kites or write novels the rest of the day, or sit in a cabin by the pond. If they aspire to more than basic sustenance, I say they should be allowed to work as hard as they like. Perhaps they don't love their work, but they love the idea of saving up for big vacations, or having savings to handle emergencies, or practicing philanthropy. Russell, born into aristocracy, didn't have to worry about sustenance and had the luxury of working hard for causes he believed in. Like him, I hope that life will continue to get better for workers. And I suppose life in the developed world today is as much better than it was in 1932 as it was then compared to the times when "fifteen hours was the ordinary day's work for a man; children sometimes did as much, and very commonly did twelve hours a day."