that should be the nature of the thing, isn't it?
I mean it should be in every relay interest to spare disk space.
I understand that relays are not required to delete, but I would say the one which does act best in his own interest and aswell in the one of the users. Also clients shall the same interest, and I think it's good to spread knowledge on the actual way this functions, to make it possibile for users to make a distinctions for what one can consider a good client or not .. just for competition you know