In contrast, he suggests that a Reed College has no such opportunity. Let's say Jobs did graduate. Then what? Maybe he'd become a professor there? What can one really get out of Reed College? More likely he'd just end up back in industry, at which point it was a waste of resources to invest in academia; a waste which Thiel would consider to be a dunce move.
No, they realized that they had a limited time-window opportunity on their hands that has a potential for a lot more value than the degree, as long as they executed on that opportunity well and had a bit of luck.
Neither Gates nor Zuck just dropped out with nothing going on for them, and only then started their respective companies. IIRC Zuck quit because he was busy running Facebook during its explosive growth phase, and he had to make a choice between allocating his time to running FB and school.
Most people who decide to drop out don't have an explosively-growing business on their hands that they have a limited time-window to execute on. And while this is a pure guess, but I don't think Zuck would drop out just because, without something like FB fighting for his time and attention.