''Did the US Supreme Court really find that African Americans are less intelligent than people of other races?''
Simple answer is no, they didn't.
The court basically found that because African-Americans had suffered a lower standard of education (their wording: ''Because they are Negroes, petitioners have long received inferior education in segregated schools, and this Court expressly recognized these differences in Gaston County v. United States, 395 U.S. 285 (1969)'') and that DP knew this the whole point of the new scheme was to continue segregation.
More here: http://en.wikipedia.org/wiki/Griggs_v._Duke_Power_Co. (it's an interesting case)
Whether that would be the same now, I don't know. On the other hand I could completely believe that companies are still worried by it, and so avoid IQ tests etc.