The New York Times has run an exhaustive piece that is worth your time to read. It is extremely long, but shows how tabloids in the Rupert Murdoch chain were all able to get exclusive stories on Prince William and Harry and several other notable British celebrities. Two journalists managed to get the PIN numbers to voice mails.
The article discusses how Scotland Yard chose to focus only on the hacking of the Royal voicemails, and chose to ignore all the other celebrities being hacked, because they did not want to antagonize Rupert Murdoch or his tabloids, with whom they have a cozy relationship.
Two News Of The World reporters were at the center of the ring, and if their tabloid did not want a particular story or if another outlet would be better, they would pass along the information to another Murdoch tabloid like The Sun.
It is a fascinating read. Thanks to everyone who sent me the link.