no it really isnt. the us is one of few nations in all of world history that never had religion run any part of the government. the fact that there are still more religious individuals than in other industrialized nations and that those people try to make laws based on their religious morals does not make the country pious. any other civ would be a better fit for piety except for babylon and korea because they have science bonuses.
Then your failure to understand American history saddens me. Original colonists aside, perhaps you should look at the original documents that form the basis of the US Government. Declaration of Independence talks about God. Bill of Rights states that there is no laws that govern what religion you may practice, opposite that of a Theocratic Nation (which is not the same as Piety). Then there is the Pledge of Allegiance which is "one nation under God".
Not to mention even before the Star Spangled Banner, My Country, 'Tis of Thee' was the original national anthem (until 1931 signed by Herbert Hoover), which includes the lyrics "Great God our King". Oh, the national motto has been "In God we Trust" since 1956.
However, let us go to the simple root of the discussion of piety vs rationalism.
pi·e·ty n;
1. reverence for God or devout fulfillment of religious obligations: a prayer full of piety.
2. the quality or state of being pious: saintly piety.
3. dutiful respect or regard for parents, homeland, etc.: filial piety.
4. a pious act, remark, belief, or the like: the pieties and sacrifices of an austere life.
ra·tion·al·ism, n;
1. The principle or habit of accepting reason as the supreme authority in matters of opinion, belief, or conduct.
2. Philosophy .
a. The doctrine that reason alone is a source of knowledge and is independent of experience.
b. (in the philosophies of Descartes, Spinoza, etc.) The doctrine that all knowledge is expressible in self-evident propositions or their consequences.
Once again, proof that Piety for America is spot on.