Okay, as the saying goes, we learn something new everyday . . . and I just learned that Danny is right and I am wrong.
Apparently, according to a PEW Research study, by the most common definition of the word, it is not RARE at all for Americans, at least, to change their beliefs. Here is a report on the research that says about half of Americans change their religion affiliation in their lifetimes.
http://pewforum.org/uploadedfiles/Topics/Religious_Affiliation/fullreport.pdf
I would qualify change of religion as a change in their core beliefs, and half of the population certainly couldn't be characterized as rare.
So, Danny you're right, I'm wrong. So it goes.