Chances are they had to pay for it, since that probably did not fall under "fair use" (they are a commercial entity, using the speech as part of their commercial purposes).
Unfortunately, the same can be said about textbook publishers, and most of them don't pay for it.
Worse, the video is much more heavily controlled by the King estate than the printed text.
http://www.foxnews.com/us/2013/08/27/transcript-martin-luthe...