So the question is, where's the line. Links for cash is not acceptable, but links for % discounts in leiu of cash is fine?
You're reaching. You can make any link about cash if you look hard enough.
Those links didn't go live as a primary condition of the discounts - it was not an exchange of discount for links. The links sure look to me like they were put up as part of the promotion, by the .edu's, for the benefit of the people who qualified. Sure the links were stretched hard by O. But that's what makes them smart IMO. They market in places that get them links. Duh.
And guess what? It works. So we can moan and complain that Google's guidelines aren't strict enough or abided by or interpreted in a way that benefits us, or we can learn and adapt.
I think though what Shadow's suggesting is that the interpretation of the guidelines is vexing. Don't let it be. Instead, figure it out and use it. Everyone else is.