Sima,
You are correct. Only the Project Manager and Manager can make changes to work item names, work, duration, dates and more as these make the Project and should not be tampered. Letting Resources change these loosens security. Making these types of changes on the Project work plan is meant to be done by the Managers, not the Resources. The resources are meant to put in time and details of work done so Resources can change fields such as Actual Effort, Remaining Effort and % Complete as well as Related Items like adding Files and Expenses, etc.