Because US copyright holders generally can't drag a foreign web site into US courts to get them to stop stealing and distributing their work, SOPA allows them to go after the ISPs, ad networks, and payment processors that are in the United States. It is a law borne of the blind logic of revenge: the movie studios can't punish the real pirates, so they are attacking the network instead.
Yesterday, Gizmodo ran a list of contact information for all the media companies that support SOPA. Like Slog tipper Vlad, I was surprised by how many publishers are on this list: I expect publishers to adhere to a higher standard when it comes to censorship, and it's disappointing to see all the big names represented here:
The good news is that the publishing industry is cowardly and fears losing customers above all else, so if they came back from their holiday breaks to mailboxes full of anti-SOPA sentiment, that could potentially make an impact.