Depends on the particular PhD program, but if you are in science or engineering in the US then you should be able to be a teaching assistant, research assistant

Depends on the particular PhD program, but if you are in science or engineering in the US then you should be able to be a teaching assistant, research assistant, or both and have free tuition and a stipend. If the author is solely talking about humanities PhDs or other types of graduate school (law, medical) in the US, then maybe the author has a point.