[lordloki]

If you include tuition at the rate undergrads pay it as part of the compensation then they are paid much more than the median wage. Average annual tuition alone for many research universities is higher than the median annual wage.

[fruffy]

For the vast majority of the degree, PhDs are not taking any classes (often, they are not even allowed to). They are just workers who either teach or research. The tuition is usually an accounting trick used by colleges/universities for tax and visa sponsorship purposes. Although faculty typically has to cover a PhD's tuition, factoring it in as pay is a little disingenuous.

If tuition was not waived, PhDs would not even apply. The way the PhD is set up in the US is a little byzantine. Other countries (Canada, continental Europe) do have normal employment contracts and benefits.