Michael,
All artifacts in the Communications module exhibit a Controlled-Hierarchy model of access. Campaigns, Groups, Messages, Surveys etc are owned by a particular user. A user like you note, can see his/her records along with the ones owned by people in his/her hierarchy. This behavior is baked into the system and must have been a business rule that was enforced when this module was built.
One solution I can see is to relax the ownership for all artifacts and allow everyone that has View, Add, Edit and Delete access to Campaigns and related records to act upon those.
AND/OR
Provide the owner of the Campaign a UI to further define how the Campaign and related records can be accessed by others (personal, allow all, restricted access)
The product managers will further research, discuss, debate and figure out, what we can do to allow better control under Communications.
Ananth