I like percy and taq's assesment and the questions are really good. Hinduism is not a fair comparison, because like Judaism it is an ethic religion that you have to be born into, sure they have some "converts" but not really in the same sense as the universalizing religions.
The Roman Catholic thing is easy to answer. I like to call it Culture. I am Irish, Bavarian, Croatian, Mexican. I am as much Culturally Catholic as I am a Catholic in faith. I would wager (if i did that sort of thing), that even in very secular nation, like say France, that the people are still very culturally catholic. That even if they do not believe in god, they know the catholic stuff, and prefer it to the madness that is protestants and Islam.
What do you think of the Baha'i? they believe in all the religions as one religion.