Wow, Narkissos, I think you hit the nail on the head!
I think that those who are more likely to leave the WT are actually on both ends of the spectrum: either those who are not yet very committed (or, in JW speech, "haven't made the truth their own" or "developed a personal relationship with Jehovah" ) and can still realise this is not their cup of tea; or those who have taken it very seriously until they realised they have been fooled, and cannot bear it.
My brothers, I think, fit into the first category--they went, but they didn't listen or study at all, never joined the ministry school, never went out in the service. They left with little in the way of repercussions and hate the JWs for their rules. Their main reason for leaving was that they wanted to be "normal."
I, on the other hand, was active as a child and young teen. Read all the literature (even the old stuff, which is where the trouble started), participated in TMS, went in the service and conducted Bible (really, JW book) studies. When I started to run into things that didn't make sense, I asked questions--and did not get satisfactory answers. When I started to research in outside publications, I discovered how wrong the doctrines were. My fade was not without repercussions--I've been called "apostate" more than once, and an "opposer" quite often--even though I was never baptized.
I care much less about being perceived as "normal" than I do about feeling comfortable in my own skin.
Meanwhile, my less-rigorously intellectual relatives, and my less-normal relatives, seem to have no problem suspending both their disbelief and their "weird-meters" and staying in the JWs.
I've also noted that those JWs who are more attracted to the "Christian" elements of the religion (which are rare--see any of Blondie's wonderful WT reviews and notice how rarely Christ's teachings are addressed as opposed to OT/"god of wrath and rules" teachings) tend to be less likely to shun. They simply ignore the society's instructions in favor of Christian love--and generally, because they toe the line in other ways, they get away with it. Meanwhile, the less Christ-like among the flock cling to the "letter of the law" and shun--even though they don't do anything else!
What a bunch of Pharisees--well, that's not entirely true. There are some Christians to be found there. They just seem to be so hung up on WT rules that Christ has a hard time reaching them through the tangle of minutia.
Jankyn