Pandora,
There's certainly a lot of truth in what you say!  But I think it's important to recognize that the drop seems worse in the RCC, and that was the point I was trying (hoping) to address.  

From what I can tell, being Catholic has long (for many at least) had a strong cultural component.  I know as I grew up, my parents tried to form me in a way that relied heavily on what the church taught.  I was strongly encouraged, for example to be an altar boy, and to "get involved" in things church.  I doubt most nones were pushed in that direction.  And I also think it important that the church's leadership continues to "double down" instead of taking a second look at some of their man-made positions (like the blanket prohibition against ABC.) That rigidity just doesn't stand up to scrutiny, which tends to lead people to see the church as more "cult-like" than as an intellectual community bound together by common beliefs and shared values.