Is wording the issue here? She didn't say the house was built "only" with slave labor, but every article I've looked at since the original post says that slaves did work on it.
Even the Wiki article says this: "The main residence, as well as foundations of the house, were built largely by enslaved and free African-American laborers, as well as employed Europeans." That conflicts with the topright article's statement that slaves were brought in to do whitewashing at the end.
I doubt this is a top search today because of people's interest in history. From the first linked article:
"In other words, even as Michelle Obama herself rebukes the nation’s history of racism, she is a living example that America has done much to overcome it."
This was stated as a criticism in the article, but it actually seems to be summarizing exactly the point Mrs. Obama was trying to make in her speech.