A university education does not mean someone will "leave" immediately, if ever. That is a myth. If that were the case I would have left 11-15 years before I did. Those that do leave because they are attending university are already questioning the organization.The GB are just plain paranoid about their constituents being better educated and smarter than they are, as any authoritarian group is.
IMHO JWs compartmentalize JW life vs. "normal" life. In their day to day normal life, they can use critical thinking skills, and become very balanced and successful people, until they are confronted with something that sets off the group think/cult programming. This causes cognitive dissonance as has been mentioned above.
Having said that, successful people do not make good robots, and very often times, with the passing of time and experience, probability dictates that something will happen to these ones that will force them to wake up. This is the real reason a college education is a problem for the WTS. College generally = success, and success = not taking bullshit.
d4g