It's still quite likely that Obama could be sworn on the Koran. You don't see the book up close, and on the outside it could look just like a Bible. Even the person swearing in might not be aware. Given that the Bible is much bigger than the Koran, it's even possible they might take a Bible, hollow it out, and put the Koran inside. Then it will look like he is being sworn in on the Bible, but inside it will be a Koran.