Incidentally found this (http://readium.org/about/project-goals):

Readium is available for both open source and proprietary applications.  For open-source, non-commercial applications, all the Readium code is available under a BSD-style license. For commercial applications,  the Readium SDK code is licensed under Gnu Affero General Public License Version 3 to help ensure the level of development and management support necessary for its ongoing development.

which I think is a misunderstanding of how public licenses work.