The program interviewed Melissa Harris-Lacewell, an associate professor of African-American Studies at Princeton University, who does a great job summarizing the significance of those three women and their roles at conventions past: Hamer, who spoke movingly to the credentials committee about having been beaten for just trying to register to vote; Jordan, the first black keynote speaker to address a convention in prime time; and Chisholm, whose run for president in the 1970s immediately followed the change in voting age, a hopeful signal that newly minted young voters might want a different kind of candidate.
When asked about the indirect reference to Martin Luther King in Obama's acceptance speech--he was referred to as a young preacher, but not by name--Harris-Lacewell put it in perspective:
I do think there’s a problem when you invoke Kennedy by name but not King by name and where you can talk about the historic moment that is Hillary Clinton’s campaign but you don't mention Shirley Chisholm. We've got to have a better historical memory as a country that allows all of the players to be there and all of us to have a place at the kind of table of American history.To find out more about black women who've made significant public speeches, check out this post on a book and recording of famous black speeches and this post on Barbara Jordan's speaking skills--she routinely ranks among the top political speakers.
UPDATE: Today's New York Times op-ed page has a column by Brent Staples on language and race that's relevant here. It speaks to the historic and current risks of eloquence for black speakers:
Forms of eloquence and assertiveness that were viewed as laudable among whites were seen as positively mutinous when practiced by people of color...It's a reminder of the power of speech, and, I hope, an encouragement to keep speaking publicly for all of us.