Corporations are at least somewhat responsible for the actions of their employees, especially when said actions could be seen as in the companies interest and were likely performed using their equipment.
If a Sony employee ran into my house with a Sony truck, I'd skip suing the individual and go right to the source. Someone there clearly let him have the keys.
While everything you said is true. I don't think the issue here is that major...it's a wiki after all.
I think the reason why a lot of sites and people are ranting on and on is because the tactic is not unlike Sony. Sony actions of late have already put them in bad light. Just a little actions of an individual will look badly upon Sony. So some degree it's Sony fault for being in such position.
Just like if you're already in a dog house because you have already forgotten your wife's birthday last week...you don't coming home drunk expecting her to greet you with a big smile.