The short answer is - the developers who use it as part of their workflow.
My personal preference is to leave the settings as they are. The bug tracker is primarily a task tracking system for the developers. It is not a forum for general discussions, etc. If you need to correct or amend a report, post a comment to the original. Individual tasks themselves cannot be deleted once submitted. However, if you feel you submitted one in error, you can request it to be closed and re-submit a different one if you so desire. Another reason to leave reports as they are submitted is to discourage the spam technique of editing a benign message shortly after creating a new topic - this is more common than you think.
If you feel strongly about this and would still like us to change the bug tracking system permissions and behavior, feel free to make your case in an email proposal to: email@example.com