The whole point of that line was to illustrate how much progress has been made in the time since the White House was built. Slaves helped build a house that a black president and his family now live in (and soon to be a female president). It was a speech, not a history lesson.

“That is the story of this country, the story that has brought me to this stage tonight, the story of generations of people who felt the lash of bondage, the shame of servitude, the sting of segregation, but who kept on striving and hoping and doing what needed to be done so that today I wake up every morning in a house that was built by slaves,” she said. “And I watch my daughters, two beautiful, intelligent, black young women playing with their dogs on the White House lawn. And because of Hillary Clinton, my daughters and all our sons and daughters now take for granted that a woman can be president of the United States.”