I guess you could say that they are only covering their own backs. There is little that an ISP can do to stop illegal Kazaa, IRC, downloads, etc. But they CAN remove known illegal content news servers.

"Being an ISP is not the easiest job at the moment. Many ISPs are forced to police their users and make sure they do not violate copyright laws, and respond to inquiries of content owners. Besides that they have to survive in a difficult market and keep their customers.

NTL a large provider in the United Kingdom has decided to drop several alt.binaries from its news servers. These news groups are used to post (illegal) software, movies and music and a place where a lot of pirates meet."

More here