I would bet this is due to some hidden variable. Maybe older or more experienced developers have a tendency to use spaces, so their compensation reflects age/level/experience, not their choice of indentation?
Never mind, reading the article sees him cover at least the experience, language, and location of the developers, and there is still a significant difference.
Maybe the team aspect made a difference, or devs worked at companies with strict style guidelines, which happened to be companies who pay well, or because that company is on their resume, they make more later on?
Maybe the team aspect made a difference, or devs worked at companies with strict style guidelines, which happened to be companies who pay well, or because that company is on their resume, they make more later on?