Ed, in this case that is quite close to the actual tagline used in all but two of the posts, so we agree on that one. And I see your point, considering the forum policies or terms of service to not specifically address taglines, but I still disagree with your argument.
1.) I don't know what the 'legal definition' of advertising is, but the general concept is quite clear: Drawing public attention to your product, service, website, etc. through the various forms of media. Traditionally that meant billboards, newspapers, 20-second commercials, etc, but now it's expanded to t-shirts, carefully-placed items in television shows, and even tattoos on people's foreheads. Advertisements are not just their own entities any longer, being inserted into otherwise germane displays. Thus, a tagline containing simply a URL is also eligible to be labeled as advertising.
2.) In all of the mod alerts I've received and discussions I've read I've never once seen the argument that an offensive post should remain because the offended individual(s) was/were not forced to read it. Just think of the number of ways people could insult you if that were to be deemed a valid reason to leave posts alone. Not one post would ever be deleted as a violation of the forum policies. In short, that's not a valid argument.
3.) Since you brought the consideration up, what is the 'legal definition' of message? Does that mean the entire post submission, verbatim, or just a particular 'message' (concept, idea, etc.) someone is trying to get across? It can be argued either way, but as enforced it is the latter. Remember, someone could have their posts deleted as spam even if no two have a single phrase in common.
4.) As you pointed out in your previous post, where would the line be drawn? At some point the taglines would overcome the rest of the post and become the 'message.' And even if that didn't happen there are those who post replies such as 'I agree!' just to avoid having their following tagline flagged. Once again we come back to "blatant advertisement."
5.) In regards to your entire 'Posting Links' argument, you cannot use it is the sole policy concerning URLs as you seem to be suggesting, for all of the forum policies apply. For instance, that section of the forum policies does not mention links to pirated content, only porn and spam. However, posts containing such are edited or deleted based on the 'Piracy or Unlawful Activities' section. Likewise for advertisements that are not for 'competing services.'
Now, as I said before, such taglines are edited/deleted based on the policy put into effect long before I joined. It's not explicitly stated in the forum policies, but neither are others such as linking to unverifiable downloads or direct linking to downloads. (Yes, there are exceptions.) I doubt anyone would file, much less win, a lawsuit against Cnet because of a deleted post, but the forum policies may be amended to include these prohibitions based on this discussion. The one thing I do not see changing, though, is the policy itself.
John