I don't even think it's a case of the legality of the two, that's not where the important difference between the two is. I think that, like Claudia said, the point is that Wikileaks release information concerning the actions of governments/diplomats/etc. people with power, and people who have the public to thank for their power. When the public are funding governments and they are acting in the name of the public then it is surely in peoples interests to know exactly what they are up to. Information shouldn't be concealed and it sets a dangerous principle when such a thing occurs.
To compare releasing footage of innocents being shot, or people being tortured, with hacking into the mobile of a dead 13 year old girl is ridiculous and it is not even remotely similar. And I know this thread is over a week old but I only just saw it and felt like commenting