In my opinion, this survey ignores the elephant in the room. Yes, slavery was a factor in holding back blacks. Of course, Jim Crow was as well. Does a residual impact from both linger? Likely. But it's also likely that the majority in these questions feel problems within the black community in the past 50 years have held it back more than systemic racism against blacks.
Of course, there is one remaining institutional form of racism facing blacks; substandard public education. Funny, no question about that either.
Photo credit: By Josiah Wedgwood (1730-1795) and either William Hackwood or Henry Webber; "Josiah Wedgewood...produced the emblem as a jasper-ware cameo at his pottery factory. Although the artist who designed and engraved the seal is unknown, the design for the cameo is attributed to William Hackwood or to Henry Webber, who were both modelers at the Wedgewood factory." (http://www.pbs.org/wgbh/aia/part2/2h67.html PBS]) (British Abolition Movement) [Public domain], via Wikimedia Commons