It may have to do with this:

FAIR USE NOTICE These pages may contain copyrighted material the use of which has not been specifically authorized by the copyright owner. In accordance with Title 17 U.S.C. Section 107, such material has been referenced to advance understanding of political, human rights, ecological, economic, scientific, moral, ethical, and social justice issues. This constitutes a "fair use" of any such material as provided for in section 107 of the US Copyright Law.