In a Telegraph News article from the UK:
The White House denied that the president bowed during a meeting on the sidelines of the London conference, though photographs show Mr Obama at least stooped significantly before the 84-year-old monarch.
"It wasn't a bow. He grasped his hand with two hands, and he's taller than King Abdullah," an Obama aide said.
What, no height compensation with the queen? She has to be shorter than the King of Saudi!