Penguin says users can’t sue

Paid Content is announcing that Kindle and NOOK users must accept arbitration instead of suing them in the pending class action lawsuits over ebook pricing. Penguin is using the rationale that users agreed to this in Amazon and Barnes and Noble’s terms of service for the ereader devices.
I am not a lawyer, but I don’t think the argument holds water. When the publishers put the agency model into effect, Amazon became their agent, not the other way around. Amazon even collected sales tax based on the publisher. It doesn’t make sense that the publisher can’t turn around and hide behind Amazon on this one.