Listened to a report yesterday that said this is the third time in history that the oath had to be redone due to a goof. The official news report released on this one was to keep everything the President signed from being tied up in court challenges because he is not authorized due to not taking the Constitutional oath. Guess who they are thinking would do that (didn't name any group, but it was pretty clear they were suggesting the Republicans would be at it)?
In Governmental affairs symbolism is as important as what you are doing. Not using the Bible says a lot to me when you are working with someone that is as polished at speaking and presentation as Mr. Obama is.