I'll draw the parallel to the Deaf community who say I am not Deaf enough to be one of them, but I'm not hearing either.  I define myself as Deaf even if some parts of the community would not accept me.  People who have absolutely no knowledge of the politics of the Deaf community would see me as being the same as the rest, perhaps no matter how I define myself.  When I achieve something that raises my profile or the profile of Deaf people, Deaf people are likely to publicly congratulate me and use me as a role model.  But the rest of the time I hover on the edge.

So, to some in black communities, Obama is not black enough.  But he self defines as black, if I understand correctly.  And to most white people he isn't white so he is black.  There just isn't enough of a conscious distinction to peg him as mixed race.  And now he's achieved this HUGE thing of becoming POTUSA he's black enough for black people too.  

That is just my perception and I have no evidence to back that up and don't want to go putting words into the mouths of other people but, that's my take on it.