Heavy users that believe to *need* the most capable computer usually have no problem paying more than what baseline model costs. MBP has "everything" they need so they're not even considering MB an option.
Students on the other hand, while obviously spending lots of time in school and thus needing a computer, are likely on a very small budget. Therefore, it makes sense to offer something that has been made "a little" cheaper by cutting a corner or two. If it's cheap enough, it's great.
What about students who really need a fast(er) computer? There's no hard data available, but I believe "nerds" that have to buy more expensive computer also do not have to buy that many books, which will likely compensate the hardware price difference. But that's mostly guessing.
You tend to put your money where your mouth is, so in other words, by spending money you tend to reveal what's important to you. If it's powerful computer, you just buy one, but if it's something else (than computers in general) you just save money on the purchase. It's really very simple come to think of it.