Cults rely on immersion. That's why the word cult often evokes an image of an isolated commune wherein members only leave to recruit or sell fruit or whatever to fund the cult. In reality, cults needn't be quite so completely immersive, but they still rely on heavy involvement of the members so that they don't have time to explore other ideas or ask questions. When completely immersed in the cult, it is also more threatening to question it. When it's your entire life, you're less likely to explore the possibility that it's false. If it's only a small piece of your life, you may be willing to examine it. College can give a fulfillment that has nothing to do with the cult and therefore lessens it's importance. It also teaches critical thinking, and exposes you to other cultures and ways of thinking. All this can lead to more introspection, which can lead to awakening.
It's a numbers game, though. You've met 2 JWs that have extended education yet remain JWs. That's called anecdotal evidence. The fact of the matter is that the more education someone has, the less religious they're likely to be. It won't destroy the faith of every one that goes to college, but a healthy percentage will leave. So regardless of the 2 examples you gave, the more JWs that get an education the fewer will remain JW.
