It's not uncommon in some circles for a daughter to be given her mother's maiden name as a middle name -- sometimes even as a first name (I know one woman whose first name is Hurley), and sometimes even in multiple generations (as in the case of the late socialite/decorator Chesbrough ("Chessy") Lewis Hall Rayner, daughter of a woman named Chesbrough Patcevitch).
But apparently Obama's mama's daddy, the furniture salesman, really really wanted a son, so he named his daughter after himself.