Most "black" Americans aren't descended solely from Africans. They've probably got some white in them, or something else. In the hundreds of years their families have been in the United States someone who wasn't solely African descended probably got into the mix. Should all those people call themselves mixed race? I'm sure a lot of people who are considered black actually have less black ancestry than Obama. Being black just means you have black features, it doesn't have much to do with your ancestors. I knew a guy who considered himself black, but I never would have even thought he was black if he hadn't mentioned it.
Point is, if you're black enough to look black, it's easiest just to tell people you're black.
"Now, a fun game should always be easy to understand - you should be able to take one look at it and know what you have to do straight away. It should be so well constructed that you can tell at a glance what your goal is and, even if you don’t succeed, you’ll blame yourself rather than the game. Moreover, the people standing around watching the game have also got to be able to enjoy it." - Shiggy