To be fair, DrChrissy's impression of how the mail is treated when proposed as a source is probably coloured by his involvement in articles on medical quackery, where the Mail has a very specific reputation. For the most part, the Mail is rejected when anyone asks, often reverted if added, but equally often just left unchallenged, because where else are people going to source celebrity gossip?
The new rule will act as a poke in the ribs to the shruggies. That's its main function.