At the risk of splitting hairs, there seems to be a certain subservience in Obama's bows that a lot of people find inappropriate. Notice the picture of Ike's bow to the Pope - they're engaged in a slight bow to each other, showing a degree of mutual respect between two heads of state that might be expected. In Nixon's picture, it's hard to tell if the two leaders are engaged in a slight bow to each other or just leaning closer to engage in conversation.
On the other hand, notice the posture of the Chinese and Japanese (shown below) heads of state; they're standing straight as he bows to them - definitely not a gesture one would expect from the leader of the world's most powerful nation.
On the other hand, we have the attitude displayed by Obama toward the Prime Minister of Canada, our immediate neighbor to the north and one of our closest allies:
I guess we shouldn't be surprised at this stuff, coming from the most inexperienced and unqualified president in the country's history. And to think the GOP couldn't come up with anyone better than McCain to run against him
