>Even campaign finance laws reflect this. Suppose you're an airline and you write off the costs of a candidate's tickets when he flies around the country campaigning. The value of those tickets must be recognized as a campaign contribution.
Ah, but you don't write off the costs of airplane tickets for the cabin staff, which is what would really fix the analogy here. Grad-students are serving as employees and trainees of their advisors. In industry, you would never, ever ask a trainee to pay twice their wages in "training costs" to their employer. They'd leave, and never look back.
I agree with people in the other thread that we really should find a way to end the legal fiction that PhD students with "tuition waivers" are being charged or paying any tuition at all. They're something between interns and entry-level employees, except of course that charging interns for the internship remains illegal.