Dunno, if person A goes to gets a PHD in distributed systems and spends 40 hours a week furthering their knowledge of computing topics, while person B spends 6 years after university uninstalling viruses from windows computers, and spends their time after work watching cartoons, it seems very plausible there would be a significant difference in their worth to a company due to a significant difference in skills, even if they are both hired on as "developers".