Even most pro-ACTA parties voted against to save their countries leaders from having to find another way out of this mess now that public opinion turned against it. Blaming the EU parliament is a relatively cheap and easy way to nullify their previous commitment (and signatures!), and one that won't result in US sanctions against individual member states.
It's basically a get-out-of-jail card for those countries that did a 180 and would no longer ratify ACTA despite signing it.
And if the Constitution Treaty hadn't been rejected by popular vote some years ago, the EP would actually have much more influence over the Commission.
The EP is a joke, a political instrument played by the same people that supported ACTA, and is now being used as a way to get out of it.
Which in all makes it more significant. In reality, it isn't so much that the EP stopped ACTA, but the people who first supported it (people with actual power) that have changed their minds, even though most of them can't admit so directly because of international (read "US") relations. In the long term, that (changing minds) is the bigger victory.