This may be a small thing, but:
I love the Irving Berlin song. I agree wholeheartedly with the sentiment. But a little chunk is hacked away from the national brain each time a president gets out of a speech not with a thought or original phrase but with this mindless pablum. This has become the political equivalent of "Have a nice day!"
Isn't this how presidents have always talked? God, no. You didn't get it from George Washington. You didn't get it from Abraham Lincoln, either in the hands-down winner as Greatest Inaugural Address Ever, his second or in that work of political haiku, Gettysburg Address. You didn't hear it from FDR.
Many of these titans spoke of God -- but when they did so, it was with some actual thought-content. For instance, from the close of Lincoln's Second Inaugural:
Fondly do we hope, fervently do we pray, that this mighty scourge of war may speedily pass away. Yet, if God wills that it continue until all the wealth piled by the bondsman's two hundred and fifty years of unrequited toil shall be sunk, and until every drop of blood drawn with the lash shall be paid by another drawn with the sword, as was said three thousand years ago, so still it must be said "the judgments of the Lord are true and righteous altogether."
With malice toward none, with charity for all, with firmness in the right as God gives us to see the right, let us strive on to finish the work we are in...
As I know first-hand, you didn't hear this from probably the most sincerely religious president of recent times, Jimmy Carter. To choose an example of a speech I was not involved in, his "crisis of confidence" speech in the summer of 1979 -- often called the "malaise" speech, though he did not use that word -- touched on spiritual issues but ended this way:
I will do my best, but I will not do it alone. Let your voice be heard. Whenever you have a chance, say something good about our country. With God's help and for the sake of our Nation, it is time for us to join hands in America. Let us commit ourselves together to a rebirth of the American spirit. Working together with our common faith we cannot fail.
But then Ronald Reagan began using the phrase to mean "The speech is over now," and ever since then politicians have seemed afraid not to tack it on, perhaps out of fear that we'll have the aural equivalent of phantom-limb pain if we don't hear the familiar words.