The FCC regs indicate obscene language is not protected by the 1st amendment in publication. It is still a fairly gray area on websites, and difficult to enforce because a lot of sites are private or overseas, etc. The Gov sites fall basically under the provisions set forth here. I can't find the specific regs (I don't have time right now). These are essentially what the blog operates under http://www.fcc.gov/cgb/consumerfacts/obscene.html

Bob is entirely withing his rights to censor posts that have anything in the posted rules, or that fall under obscenity regs. Direct attacks get a lot of posts removed - not references to someone making a comment and addressing it directly, but pointed attacks. Most phrases that indicate the usage of obscenity (CYA ..., etc) fall under the same guidelines.