Sadly, in the US it's common to sue everybody who has some relationship to a case. The idea is that somebody must have deep pockets, and will either settle or you might get lucky to have the court declare the liability "joint and several," i.e., the full responsibility of all of the people getting sued (see, for instance, http://www.coyoteblog.com/coyote_blog/2009/05/the-state-of-t... ).

Better link: http://www.coyoteblog.com/coyote_blog/2005/08/the_everwideni... . And, of course, http://www.law.cornell.edu/wex/joint_and_several_liability .