The text is from [[MediaWiki:History copyright]]. The text on the English Wikipedia was added by Jamesday last year following a discussion on this mailing list where Tim made the addition to the history footers possible. See http://mail.wikimedia.org/pipermail/wikien-l/2004-June/013706.html
There is also related discussion at http://en.wikipedia.org/wiki/Wikipedia_talk:Terms_of_use#Title_17
Information is also at http://en.wikipedia.org/wiki/Wikipedia:Page_history which states the Wikimedia Foundation's official view on this matter. See this diff which Anthere and Jimmy both agreed to lasy July - http://en.wikipedia.org/w/index.php?title=Wikipedia:Page_history&diff=48...
Angela.