You do not need to mention "all" contributors.
A satisfactory attribution is merely a URL pointing to the Wikipedia
article and possibly one pointing at the history page.
By our inaction we've made it clear you do not need to directly mention any
contributors.
Will Johnson
In a message dated 8/18/2009 9:29:21 A.M. Pacific Daylight Time,
brewhaha(a)freenet.edmonton.ab.ca writes:
To my knowledge, all that is
required to meet a -BY- requirement is one mention of all contributors.