I think you 'nailed' it. If IP was used to shut down the site, I doubt that it was the main driving force given the many other sites that are using photos and videos and are known and frequented by the writers/actors/agents. The site owners were also claiming there was more than IP involved in the C&D letter/lawsuit. But IP might have been used as the hammer - IP is becoming the 'go to' tool for many corporations/groups to silence critical speech. (see the ACLU case I listed in my last link above).