Maybe for their first jobs in industry. But assuming they aren't in academia, I'm betting a PhD in an in-demand CS field will be making a lot more than someone

Maybe for their first jobs in industry. But assuming they aren't in academia, I'm betting a PhD in an in-demand CS field will be making a lot more than someone with a BS and 5 extra years experience in a few years. Not to mention that for the type of jobs that require a PhD, the 5 years it takes is 5 years of relevant experience. And there are many jobs that are effectively closed to people without PhDs regardless of how much experience they have.