WHOOSH...That's the sound of the tongue-in-cheek message going over everyone's head who missed the humor here. Chris Rock is not criticizing Barak Obama for acting white, he's "reassuring" nervous conservative white voters who don't feel comfortable voting for Barack Obama (and distrust minorities in general) that Barack Obama really isn't so different from them.
Far from adhering to black stereotypes, Barack Obama fits the white stereotype that should feel comfortable to conservative whites and reassure them. He's doing it with humor and wit because he's a talented comedian.
There's no inherent criticism of Barack Obama in pointing out that he fits the white family stereotype (small family) even better than the superwhite Romneys (5 children and 14 grandchildren). Nor is there harm in reminding conservatives (again with humor) that in fact Obama was raised by white grandparents in a value system that should reassure conservative whites, even using the name "Barry" when he was young. This in no way negates Obama's self-identification with the black community as a mature adult (he did after all resume using Barack when he grew comfortable with his on identity upon maturing, marry a black woman, etc). Don't lose sight that the sarcasm here is leveled at making uptight whites that balk at voting for minorities feel that minorities are not so different from whites after all.
The message here, told with humor, is ....hey, he's not so scary, is he?
Chris Rock is not saying that Barack Obama is acting white to please whites at all. He's actually saying that Obama is what he is and he doesn't fit either the black stereotype of what a black president should be, nor does he fit the white stereotype of a black president-- a threat to white society. Using humor to convey the point is effective and thought-provoking.