I have already discussed this with Stefan, he does not approve of the logging of personal messages unless there is a specific reason. In those cases its been to confirm whether someone is participating in an illegal activity or is a threat to Graal security. Its rare and targeted. Staff pm's are also logged on occasion while on tag to determine if they are abusing chat commands. This is something they are usually fully aware of though.
I'm fairly certain that on the larger games where history is recorded the staff that can access it have to sign a confidentiality agreement. I believe some of the former global staff also had to sign an agreement. To my knowledge that hasn't been done since Ibonic though. IF such loggings were to ever be put in place again, I would hope that is something that would be required for anyone having access to the information.
Quite often people exchange more personal information such as addresses or phone numbers through private message and I would prefer that not be something given freely to the public by someone that couldn't be held accountable for their actions.