Depends on the university. 25 years ago now but a number of the PhD students I worked with had mummy and daddy paying for everything. One enterprising guy had a side business selling cocaine. Most were slumming it in house shares and taking on casual work. Only the blessed had teaching appointments. I was blessed until I realised it was a curse.

I meant that most labs and tutorials were run by PhD students, not that most PhD students had jobs running labs and tutorials.