I think this whole article (and the other stories I've read like it) is best summed up by the last sentence: "In other news, pencil company gets sued because someone writes angry letters using pencils"
The lawsuit is asking Wordpress to take down the posts or the blog, which is well within Wordpress' power.
I'm trying to avoid making a third analogy, because analogy usually takes you further from the specifics, but apparently I can't help it: It's analogous to suing YouTube when a user uploads copyrighted content. What is YouTube's responsibility to stop serving up the "illegal" content? Or a mail host's responsibility to stop customers from sending spam?
Hosts can not wash their hands of the content that they're sending out just because it was user-generated.
My point was not that both crimes were equivalent. My point was that "a user did it!" is not a defense against lawsuits.