It doesn't seem to me to be as simple as what can be summed up in a yes or no question. People have been religious for eons. To me, JWs are simply another religion and as such are similar to other people who believe strongly in a religion. It seems to take a certain mindset to accept that which is unprovable. This has been explained scientifically several times.
It's true that their particular brand is radical and requires more closing down of one's mind, but they are offered a complex theology, lots of study, and opportunities for importance in the congregations (where else can a blue-collar worker be granted such importance as clergy sans degrees, etc.?). To me, the more fundamentalist a religion, the more closed mindset is necessary.
It's a voluntary close mindedness, but is considered greatly necessary by one's peer group. It's a closed system and, while they're free to read widely, it's also a high-mind-control group that precludes such investigation outside of the cult-type literature. The community is very exclusive and closely knit so that one risks much to be open in their investigation.
It's very complicated I think and, while they may attract (or rabidly pursue) less-educated people, it seems to me to be more of a case of the Stanley Milgram experiment wherein the college students blindly "shocked" people because of being ordered to do so by an authority figure. It wasn't that they were more stupid than the ones who refused, though they did find out the more educated a person was, the less likely the were to follow blindly. This was attributed to better self-esteem and trust in their own judgment when more educated. That may also be why JWs are able to dupe people in traumatic situations.
Once they're hooked, it's more difficult to extract oneself because of the close-knit community.