What I'm meaning, though, is that if you were to go against your duty as the head of NASA, Carl Sagan isn't going to rise from the grave and smite you for your transgression. Whereas I believe that is exactly the point of swearing over a bible.
I'm not meaning to say it's meaningless to swear over an important book (or that it doesn't make some kind of point), rather that an important element of what it means to swear over a religious text is lost. The whole point of rationalism is that the universe isn't sentient and won't and cannot judge your actions.
An oath is a promise to someone that you will act for the greater good, and you do so with your hand over a representation of who will witness and judge you for that.
I don't really know if I'm trying to say anything in particular. It's just some thoughts I had when reading.