Commercial sites are afforded less 1 st Amendment protection. Obscenity is not protected speech. If you can buy it legally in print in a store, then it is not considered illegal or obscene for adults. One issue that has not been tested is the college student who is under age eighteen. Copyright laws DO apply to the web.
Publishers are liable same as the author.
ISP s are currently not considered to be publishers, only distributors. Economics drives American copyright laws. Fiction is typically protected more than factual material. Web site should link to your copyright policy. Must get permission from intellectual property owner.