Tuition should be covered by grant funding (RA) or the department (TA). If a university "accepts" you in a science/engineering PhD program, but is not offering tuition and salary, they're really saying they can't take you. Note that at many universities, students will cost a grant more than postdocs for this reason.
I think his point was that if you don't consider your salary as your take home pay plus the tuition that is paid on your behalf, then it is a very meager income.
