Weirdly, instead of the usual system where everyone gets a license from the original copyright holder, this grants everyone the right to sublicense under the same agreement. I think it has much the same effect, but it's*weird*, so I don't know.
I think I remember being told that this is a normal habit of English copyright lawyers, but it has a similar effect. I wish I remembered whether there were any differences.
-- MJR/slef My Opinion Only and possibly not of any group I know. http://mjr.towers.org.uk/ http://www.ttllp.co.uk/ for creative copyleft computing