I agree to a certain degree that it can be based on personality. Some personalities are just ok with going along with the crowd. If they are told it is the truth, they will not question, they really don't care either way. If they are happy with what they know to be the truth, then why research it?
On the other hand, there are those whose personalities question everything in existence and don't just do as they are told. They have an innate sense of what they feel is not right and will research the crap out of it to find out whether or not what they are being told is the truth or not. From politics to religion to buying a new car!
Agreed as well though that it is a mindset on what has been spoken over and over again, not to question something they are told to be the truth, only to believe that it is the truth. As a born in, this was driven into my mind for 39 years of the 44 that I have been alive. It is only when you break free from this mindset, that your instincts really start kicking in. Breaking free for me came from being wrongfully disfellowshipped. I started to question the unloving way the elders treated my situation, then began questioning if they could treat someone like that, then was God really with them. That lead me down the path to learning for myself whether or not I believed in a God...still questioning, still researching, still learning.
I heard the same things from my x-husband when I would tell him certain things that I had read or saw here on this site. For example, one time I told him I had a copy of the elder's book. He told me that just because it was posted, didn't mean that someone didn't go in and change it to fit their "agenda" against the watchtower. Again, that comes from many years of being told that apostates have an agenda and are willing to go to any lengths to get you to turn away from the organization, lying to you about "truths" just to get you to turn away from Jah.