I think the point being made was that you can only do this if the owners of those works let you (or you intend to claim fair use). If they had been required to license all works that were incorporated, that would likely have severely changed the speech, so the fact that it is what it is is largely due to the fact that they were able to lift all that material. Yet that same opportunity is now being denied others.
Indeed the copyright status of derivative works is somewhat controversial. Perhaps one of the most famous examples of the issue is The Grey Album by Danger Mouse (2004) which heavily sampled both The Beatles and Jay-Z. EMI was very keen on stopping the distribution of the (then) unknown, underground album, however they have given up eventually after facing widespread public outrage.
