Comment 7 for bug 768352

Series and project drivers can edit milestones. Series drivers can create milestones (project drivers probably should be able to too). Project drivers can create series. Project drivers can edit and administer blueprints, including their series targets. Project drivers can target bugs to series.

Your statement that they have no additional powers is clearly absolutely false, and they probably have other powers that I cannot immediately recall. The driver is a release management role; their powers largely pertain to release management. Bug statuses are controlled by a separate role, the bug supervisor.