I find it interesting that the question that's arising is "should there have been a copyright notice", rather than "should it have been posted at all". This was a reasonably sizable chunk of Walt's work, and it was not done in a journalistic context of commenting on the work itself in any significant way. I certainly have a soft spot for Boston Charlie (and Pogo as a whole), and can't say I was saddened to see those words and show them to my new wife without having to yank the book out of somewhere. But if we're going to talk about creator's rights, I'd say that the reuse of a creator's material on a commercially-funded site without any visible sign of granted permission should raise a red flag right there.