Couldn't say he didn't ask for it...
The hack was performed recently in the midst of Facebook holding its "Hacker's Cup". So it can't be said that no one saw this coming; thousands of hackers from all over the world were invited to take part in activities to prove their cred.
So while all these programmers, hackers and hobbyists were invited to the server, Mark's page became the target. Not very much was modified on the page apart from some posts that were rather non-supportive of the recent interactions between the social networking site and the banks of the US.
For more on the story, check out the Guardian.