America was not founded as a religious country. AT ALL.
Jefferson, Washington, Franklin, Madison. None of them were Christians. Jefferson openly hated Christianity. Quotes include:
-I do not find in orthodox Christianity one redeeming feature.
-It does me no injury for my neighbor to say there are twenty gods or no God. (secularism)
The "In God We Trust" wasn't added to a coin until 1864, and it wasn't a motto until 1956.
The Treaty of Tripoli specifically states we weren't founded on Christian beliefs.
Also, nonreligious people are more numerous in America than Jews, Blacks, and Gays. Not a real minority. Statistically speaking, we must have a few people in Washington right now who don't believe in a god.
/rant
On topic, as an atheist, I really don't mind Obama saying it for his own personal reasons. If it was mandatory (which it isn't), then I would find issue with it.