Briefly...
Sure, individual blacks may succeed. But as a group?
To my mind, blacks in America do not represent a permanent underclass. Mobility into the middle and upper economic classes is possible for black men and women in America. Is it more difficult for them than for whites? On average, yes.
Imagine being a black boy growing up with jokes like this being told by your mom. Would you feel motivated to even try? Many don't, and the cycle continues for another generation.
Women who are fond of jokes like that often have personal experiences that enhance the meaning. I would think, though, that if a young child were to hear his mother tell such a joke, he could take it as a counter example of how to behave differently to make his mother happy.
As far as I've seen, this does not happen on a large scale in Canada.
I'll not argue with your observations.
All I can say is that the difficulties faced by blacks in America are much less than they were about 5 decades ago. Poverty in America has much less to do with race than it did about 5 decades ago.
In college I read [link|http://www.pbs.org/fmc/interviews/wilson.htm|William Julius Wilson]'s [link|http://www.amazon.com/exec/obidos/tg/detail/-/0226901297/103-9187968-0443030?v=glance|The Declining Significance of Race]. Although I don't recall much of the details, I think he presents a strong case that the title is correct.
FWIW.
Cheers,
Scott.