I agree with Michelle. Why exactly does it matter to you? You obviously dislike Obama, from seeing your other posts. I don't understand what you're getting at here. Do you think he should call himself white because he had a "white upbringing?" Do you feel rebuffed that he calls himself black? "White" is very exclusive in our U.S. society. If you are biracial, and call yourself biracial, even when just answering the question, "what is your background?" you will get scoffed at by members of the non-white race(s) you belong to and be accused of trying to be better than the plain old black/Latino that you are. It's a no win situation. It's obviously a very personal matter. I don't know or care why Obama chooses to identify as black, though I'm guessing he had similar experiences to mine growing up which influenced him.
I don't understand the nitpicking on non-political issues when it comes to Obama. It seems that some conservatives want to find any little thing to be bothered by and use to get to internal fears that many whites have (or that they feel they have anyway) about voting for a black man. You may not be doing that, but I see similar seemingly genuine questions about Obama on forums that end up coming from Obama haters as a way to try to drum up support.