While John's intent was to show that most Christians would lose their faith after a short time away from their group it reminded me of an incident that happened to me several years ago. My wife and I were invited to a Thanksgiving dinner at her aunt's church. I was still in my "angry at the Church" phase, but I decided to go along with it to be polite and hey, why pass up free food. As we were walking up to the church I kept asking myself "Why would anyone want to go to a church week in and week out anyways?"
For you Christianity is your social life. That's all it is. That's all it ever is... You believe because you worship in a community of other believers who give meaning to your life. Take you out of that community for a few months or more, read some books, and your faith could suffer and even die. A faith like yours should be sustainable apart from the Christian community of believers but you'll never attempt this, will you?
Then something very odd came to me. One single word: TRIBE. Churches have managed to completely replace tribes over the centuries. After Man decided that the hunter-gatherer lifestyle was too costly they switched to an agrarian culture. This agrarian culture allowed Man to urbanize but completely killed the tribe concept. People still had their extended families to rely on but the large tribe of many families that needed one another was gone.
So, what stepped in and took the place of the Tribe? Organized religion of course. Churches have become a social division of like-minded people. Belonging to a church means belonging to a super-extended family that cares about your well being. That's one of the ways that the super meme of organized religion has propagated over the years, by becoming powerful social clubs that help and protect its members.
This makes it very hard for people to willing leave church groups. The socialization and protection is more valuable than principles and beliefs. When church beliefs and personal beliefs no longer match up a person is forced to either speak up (and risk being forced out) or be quiet about it (and remain in the group). From personal experience I would say that roughly 75% of church goers do not agree with their church's doctrinal message. This is mostly due to laypeople being ignorant about what church doctrine really says. However there has to be a large group of people who know the doctrine, disagree with it, but remain in order to take advantage of the social group.
Sadly I doubt there is anyway to test the theory because no one would be this honest on a questionnaire.