Well, the obvious.  It's President Obama, rather than President Bush.

But there's something else.

Scour photos of the Oval Office over the last eight years and there is one thing you won't see — a man sans jacket.  That's because Bush had a rule — jackets always in the Oval Office. 

Obama, consciously or subconsciously in keeping with his roll-up-our-sleeves attitude, has dispensed with that rule rather quickly.