Edit: Added after the jrockway and tylerhowath replied, but didn't want to reply to both:
From the Apple Sales and Refund Policy… Purchases from the Apple Store for Education Individuals are not for institutional purchase or resale.
I presume the same applies to the in store discount. Apple has enough lawyers to cross that "t".
Considering I was a big Apple fanboi when I was in college and I've never signed a legal document in an Apple store, my guess is that it's the first one.
There is no check for the student pricing. You are however limited to buying one computer a year with the discount. So if you try to buy another computer within a year using an education discount with the same DL, you will be denied the discount.
I'm sure it's either in, or incorporated by reference, that text that people don't read about accepting conditions of a sale.
In practice, Apple can't afford to sue every weasely kid who thinks he's entitled to free money for being clever. So they also restrict it to one computer a year and take their losses on the young criminal masterminds.