With Subversion one can setup access permissions per directory within repository. So eg. one group can have commit access to directory A, read on B - with exception that DevA has also commit permissions on B.
How can one setup such a structure and permissions for Git repositories?
Gitosis can help you there. (The page seems to be down currently but the source is still available at http://eagain.net/gitweb/?p=gitosis.git.)