Maybe someone can answer a question I've long had: in a BSD licensed library, isn't the copyright distributed over all collective author's, not just he one list

Maybe someone can answer a question I've long had: in a BSD licensed library, isn't the copyright distributed over all collective author's, not just he one listed in the license? That's why some projects make people sign agreements stating that they send copyright to a foundation right? I never understand why it's not standard practice to say "(C) Copyright 2011, Please see authors.txt for a list of people"