Episode 79 of the West Wing saw the same dilemma with poor Charlie running from pillar to post and almost no bible at the end. But still, when it came down to it, one bible.
But more fundamentally, it points to Obama's entirely secular nature. When you take an oath with hand on the bible you are calling on God to witness that oath. What Obama was doing, instead, was calling on Abraham Lincoln and Martin Luther King Jnr. And while he may have the despotic character of Lincoln he has nothing in common with MLK.