I think the arrests of police officers leaking to the press was because it was an investigation about the press, which would be similar to someone in the Met alerting paedophiles who might be arrested.
At least these leak/s are to the public and perhaps it is to inform us that the evidence might now be strong enough to arrest those involved. Why they are not arrested now, rather than in a few weeks, is strange. Will it happen?
There have been arrests unrelated to phone hacking.
Why leak ? If the police want coverage in the media issue a statement or call a press conference. With claims of cover-ups etc seems daft to leak such things from under a cloak.