They support him first because of his welfare socialist giveaway programs. Being black is just icing on the cake.
Blacks would not give Allen West 10% of the vote if he were on top of the GOP ticket instead of Romney. 90% of blacks are democrats because of socialist programs. Never forget that Bill Clinton and Al Gore got about as many black votes as the Kenyan candy man. Also never forget that the Kenyan can get 100% of black votes and Romney can still be elected.
Whites elect the president. Whites outnumber blacks by 70% to around 13% of the total population, but if you were to look at American sports and entertainment you would think the percentages were the other way around. For the last 30 years the majority of blacks were born to unwed mothers and had no father figure in their life so they looked up to athletes as role models. You still see very few in highly technical fields, such as doctors, nuclear engineers, or aircraft pilots. The reason for that is the breakdown of the nuclear family and the democrats keeping them dependent on the government instead of self-reliance.
On average, blacks don't have the raw intelligence to be competitive in these fields, in the same way that whites don't have the raw athleticism to be competitive with blacks in a lot of sports. People from white trash backgrounds routinely outscore the children of senior black corporate execs (many promoted via affirmative action), so culture is not the issue. A big part of the drama with respect to race differentials comes from the fact that the different races don't look the same. If there was a way to genetically engineer all white babies at birth so they would all grow up with black features or vice versa, nobody would care, and we'd accept the disparities as part of the normal distribution of characteristics within the human species.
The reality is that on average, different races have different raw abilities, much as German shepherds and chihuahuas are wired differently, despite being of the same species. It's not impossible that a Japanese runner could break the 100m world record, but it's not very likely. Similarly, it's not impossible that a black person could be the next Einstein, but it's not very likely.
What makes these inter-racial differences problematic in this country is a combination of our past history of slavery followed up by a century of Jim Crow. Without Jim Crow, blacks would be much more fully integrated than they are today. For one thing, miscegenation over a century would have ensured the practical disappearance of the color line. But that's all water under the bridge, and our predicament is what it is.