Note that the Staff Ethos is a guideline and it is stated that it is in the post itself.
With that being said I don't know why a admin can't own up and slay themselves if they RDM. One report for RDM on the forums is usually DENIED as it is a mistake and the handling LT won't accept it. If a staff member is slayed it makes the staff look a lot like the users and puts them on an even punishment ground which will put them closer and not make staff look like they do no wrong. Beyond that most of the time mistakes are punished anyway because it's easier to just slay everyone instead of making the hard choice and have someone scream at you about it.