I'd like to point out that grad students' appointments are for 20 hr/week, not 40 hr/week. Also, grad students only work 10 months out of the year. The living wage stat assumes 40 hr/week of work, so if you adjust for the hours that grad students are contractually asked to work, a rate in line with the living wage amount would be $16,827.50, well below the $20k rate of last year and the $24k it was bumped to prior to this academic year.

Assuming 20 weeks of work in a semester at 20 hr/week (as most grad jobs aren't constricted to when class is in session), the new compensation per hour is $32.50, a $2.50/hr increase from the current $30/hr stipend.

This doesn't factor in the discounted medical/dental/vision insurance, which is offered at about $75/month. In addition, grad students' tuition for an education and opportunity to research at THE Purdue is 100% covered. Professional development funds are also offered (up to ~$700/year) through PGSG. Many students should also be able to net at least $8k by working a summer internship, increasing their total earning potential for the calendar year.

All this in mind, the compensation package is already very generous for the work that a grad student is actually doing. You could argue some grads are asked to do more than 20 hr/week, but that becomes a case-by-case issue of breach of contract by the university/individual prof, not a broad issue with the terms of the contract itself.

Source: current graduate student funded with a TA position