> Having a PhD offers no such guarantee in the federal government.
I misread the GS site, you are correct.
Still quite a bit above the median in terms of salary, which was my only real point (and that if you are primarily motivated by money, advanced degrees and Federal government employment is probably not in your future, anyway).
The GS grades are not about education, but job responsibility. The grade for a given position also depends on the agency you're working for and where. An engineer with the AF working for ACC might be a GS-11, but a GS-12 if they switched to AFMC, or GS-13 if they did the same job with AFMC at another base.