Oh, shut up, Bill. Sometimes you're just as bad as Jerry Falwell!
The President recognizes that there are more people celebrating holidays at this time of year than just Christians. Since he is President of ALL the people, it stands to reason he'd wish a generic holiday greeting so that everyone would feel included. On the INSIDE of the card is an Old Testament passage; one that should satisfy all Judeo-Christians as it comes from the book which they revere above all others.