2 words Affirmative Action
No, there are some other points.
1. A lot of blacks are not able to earn their living, so they think, that Obama will redistribute money to them via welfare.
2. They think too, that they will get free health insurence if Obama is elected.
3. They have great problems with their sexual ethic, so Obama will be ensure that they can kill their babies easier.
4. A lot of black people are involved in all kind of crime. They exspect from Obama, that the police will be handicapped and that the judges will be more mild to blacks.
5. I think in their heart they hate the bible with the strict morals and in their so called churches is preached mainly social justice and black liberation theology. So Obama stands for the contempt of biblical values and they hope to get a moral backup from him.
This are no legitimate reasons in our eyes, but in the eyes of his supporters, they are.