http://www.publaw.com/joint.html

Wikipedia is a clear case of co-authorship, and Bomis is not only the publisher but a co-author, since its employees are authors. Joint authorship standards assert that any co-author may claim authorship over the entire work, even if that author has only contributed to one particular section.

In other words, any author (including Bomis) can sue in the case of infringement of any article in Wikipedia, even if they didn't contribute to that particular article.

The statement that Bomis is a co-author assumes that Wales & Sanger are working for hire, which is automatically the case unless they have an explicit agreement otherwise.

Also, as has previously been discussed, copyright is not transferrable without a signed contract, even if there's a checkbox upon initial submission.

(see http://www.loc.gov/copyright/circs/circ1.html#toc)

I have no idea how damages would he dealt with. Probably injunctions is just about all that could be sued for.