Dear God, you don't get it. First, she was wearing a formal dress that showed cleavage, the dress was entirely appropriate. If she was wearing a thong and bra too the function that would be different. Second, what the hell do you think people are looking at in that Obama picture, his shorts? They are looking at his shirtless chest and abs, he didn't go topless on the beach because "that's what you do." He did it precisely because he knows he's got a decent enough body and that it will play well with the press. Let me ask you this, in all the time since that photo Obama has routinely gone to Hawaii (his home state) to vacation with his family yet have you ever seen any other shirtless Obama beach pics? The answer is no.
In fact, here's a picture of him post-election on vacation with his family:
That's right, he's wearing a shirt because the election politics are over and there's no need to play that card again. I just can't understand how naive you have to be to not understand that NOTHING a presidential candidate, or any serious politician for that matter, is spontaneous or done without deliberate precision. Do you think when the walk into restaurants to get some food and take pictures with all the customers and staff that wasn't planned weeks in advance?
The Obama beach pic is the EXACT equivalent to the dress cleavage picture, both of them know exactly what they are doing and know it plays well with voters. It's all apart of the political game, like how male politicians in American roll up their sleeves when they speak in rural areas so as to make it look like they're just a working guy. The fact that there is this huge controversy because a women is playing the same game says something.
EDIT:
Actually I did some rechecking, turns out that photo with him at the beach with his shirt on is part of another vacation prior to the 2008 DNC. I actually cannot find a single beach vacation photo of Obama after his election despite that he has taken one every year.