In reply to Ryan McCue.

If done properly, the copyright notices referred to in the GPL should note who the copyright holders are so attribution is, in that sense, correct. You're quite right, however, that in a large project like WordPress it's impossible to mention all contributors by name. That's why a WordPress download refers to "the contributors" rather than to everyone by name; everyone seems to be OK with that. This is what the license.txt file actually says:

"WordPress – Web publishing software Copyright 2011 by the contributors
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
...
This program incorporates work covered by the following copyright and permission notices:
b2 is (c) 2001, 2002 Michel Valdrighi – m@tidakada.com – http://tidakada.com Wherever third party code has been used, credit has been given in the code’s  comments.
b2 is released under the GPL and
WordPress – Web publishing software Copyright 2003-2010 by the contributors WordPress is released under the GPL”

If you're interested, I've given my legally-oriented thoughts in "Some thoughts on the Wix mobile app story" at http://wpandlegalstuff.com/some-thoughts-on-the-wix-mobile-app-story/