Hi,
Publishers and Administrators can see and update/delete any existing services. From this perspective, it does not add much to create separate groups of Publishers/Administrators. Some people want better control, so for example a particular publisher can only edit/delete services that he/she created. This is something that we have enabled in ArcGIS 10.2 for Server, when used in combination (Federated with Portal) with the Portal for ArcGIS extension.
Ismael