It's rather unimpressive to claim that you can tell a customer that "your sysadmin had authorized access to all data, so any of it could have been copied".
(USB ports / CDs being what failed in the Bradley Manning case)
Theoretically it's trivial to audit sysadmins. In practice it's virtually impossible. Let me know when Red Hat wants to bet money on it.
It's rather embarrassing have your IT supplier tell you "This other person who you trusted with access to all your data may have copied some or all of it -- you should trust your employees more granularly."
The real issue is who cares about this (the information collected)
I've seen this with "limited administrators" where they were audited by senior people.
But there's always a point from where the trust is "absolute"