As a former grad student, I am not at all surprised by this. Academia is a very personality-driven world where prestige, connections, and social capital matter at least as much as the quality of one's work. The prestige, influence, and connections of one's department and dissertation advisor make a huge difference, and the most prestigious advisors tend to work at the most prestigious universities.

In a job market with so few openings, especially in the humanities, this clearly has a distorting effect. I suspect that if the job market were not so bad, the effects described in this study would be reduced.