As I have shown at
http://de.wikipedia.org/wiki/Benutzer:Historiograf/GNU_FDL_Highway_to_Hell_-...
it is a myth that only the 5 main authors have to be mentioned according the GFDL. This refers only to the title page and I cannot see such a thing like a title page in the Wikipedia.
You have to read the license carefully. The principle of attribution is codified in the preamble. "Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others." If there would be only an obligation to mention the 5 main authors this wouldn't make sense.
The ADDENDUM gives the model for attribution for GFDL contributions:
"To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: Copyright (c) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License"."
If you are verbatim copying you have to copy 1:1, id est to keep all sections including the section history with the collection of copyright notices according the ADDENDUM. In the notices are fields with the names of the authors.
For modifications there are the following relevant rules:
"D. Preserve all the copyright notices of the Document."
"I. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence."
The WMF opinion that the version history isn't the section history is clearly wrong. After each modification something has to be added to the section history OR the section history has to be created. Thus one can only conclude that the section history is the version history.
A line in the version history is both copyright notice and part of the section history.
Wikipedia is a de facto anonymous colloborative work with the wrong license. CC-BY-SA would be the right license if and only if BY only refers to Wikipedia but not to the myriad of authors.
Klaus Graf