@doug: the copyright issue is essential but only one part of the story (at least for German law?); the copyright holder may not do with "his" image what he'd like to do if this affects the personal rights of the depicted person; that is "transfer of the image rights " including publishing has to be agreed as well.
most model releases consequently contain a) explicit transfer of copyright and b) explicit transfer of f.i. publishing rights to the photographer, retaining similar publishing rights for (unaltered) images to the model. commercial issues are mainly to be negociated independently.

I think a model release has to be distinguished properly from a contract for work and labour with a photographer, f.i. for portraits or a wedding - that is what Zachary is asking for in my view...

Gerald