America is deeply rooted in religion, as most of the early settlers of the region were radicals looking to build religious utopias. America had multiple "Great Awakenings" which showed a revitalization of religion in one way or another while the rest of the world didn't see the same thing. If you know about biology, it's kind of like the founder's effect in evolution. A small population (the super religious in this case) break off from a larger population and form their own colony, literally. The new colony is separated from the original population (the Atlantic separated America from Europe and Asia and really hampered the flow of ideas until now with the Internet) and their qualities become more pronounced.
The focus on religion is slowly slowly dissipating as the world and America becomes more global, in a sense.