I don't know the original source of this statistic, so it could very well be incorrect, and how they determined this I don't know but...
I've heard it said that only 10% of the population actually thinks for themselves. The other 90% just go along with what they've been told from others. (I'm not commenting on anyone in particular before someone starts to get defensive)
I think this is true within the church as well as outside of it. I think though that it's more obvious within the church because if we really believe it we should be able to say why, as well be knowledgeable about the particulars of the faith and probably some of it's history.
People tend to be lazy as a rule, so unless they have a particular reason to work at something, they tend not to. There are a lot of people in churches who just go by what the pastor said on sunday, and that's all the knowledge they have. It's depressing but true.
As a theist whose completely addicted to books and the search of knowledge, I won't take offense because you didn't say all theists. But I agree that many within the church need to wake up and really look at what they claim to believe.