$500 desktop can have roughly 2.5x the performance that a $1000 laptop has when you build it yourself. This means you could potentially buy a laptop and a desktop for the same budget and have the high performance when you need it and a laptop to work around campus on less demanding tasks.
This is exactly what I was going to say. The OP's bias for laptops is pretty clear, for one he doesn't even mention price anywhere. And to say desktops are "old" and laptops have "just about the same if not more power" is just laughable, because you'd have to pay 3x the price of the desktop for that to be the case. And at that price point, you may as well buy both a desktop and laptop which would still be cheaper than a single "powerful" laptop.