tigris.org has a hierarchical role-based permission system (a user has a role in a project), which is separate from commit access to Subversion's repository. Being a Subversion full committer doesn't imply you're given the Project Owner role. Active full committers who have participated in the project for more than six months are eligible for tigris.org's Project Owner role, which grants them the ability to manipulate various additional features of the site. This role is not doled out immediately because of the power it gives to accidentally re-arrange things on the site, and because of the site's incomplete review/audit trail.
tigris.org users are granted the Project Owner role by way of membership in the svn user group.