Laws are only one aspect which governs how we conduct ourselves. Just because it is legal doesn't mean something is right, or the even best option.
Example 1: the so-called "interview" of Iraqi prisoners by Australian intelligence officials. It may be semantically legal, but no one really doubts the Iraqis were beaten up.1
Example 2: Not apologizing for the detention of Cornelia Rau when it was clearly the "right thing to do", even if there are legal implications.
Example 3: The "right thing to do" defense has been used by the Government before though: in the case of the invasion of Iraq, and the sending of troops to East Timor when both were on questionable legal grounds.2
Conduct can also be governed informally through responsibility to one's community. For instance, members of the Muslim community was quoted to have said "Mamdouh Habib owes an explanation to the Australian Muslim community what he was doing in Afghanistan". That's a pretty legitimate expectation, given that all Muslims may be unfairly tarred with the terrorist brush by the questionable acts of one person.
The other one is simply of conventions - like not misleading the parliament. With both upper and lower house majority, the leader could get away with anything really, even lying. Looking at how John Howard had avoided trying to mislead the parliament by having layers of advisers and passing off questions to his ministers, I'm not certain what he's trying to achieve. He's only lessening his place in history by not being a real leader. Furthermore, he's not really endearing himself to his ministers. Costello and Hill are the kind of decent people one would invite home for dinner. 1
I'm impressed by the fact that Australians are more willing to act as whistleblowers compared to their American counterpart. Cynicism triumphs over jingoism. 2
The only distinguishing feature between (2) and (3) is that Indonesia and Iraq were unlikely to sue the Australian Government.