You are totally right when you say it's not about copyright, especially if you are currently residing in the United States where the origin of copyrights are to be found in a really nice and sensibe constitutional clause. In France however it's the moral rights of the author being what the copyright legislation is being centerd around, so there it would be about copyright. In the UK copyright originates from allowing the Throne to commit censorship, so that's neither about moral rights nor about economical rights. It's about political rights.

Plagiarism however, is plagiarism. Theft is Theft, and infringement is infringement. All three totally different "things", that's the tree i'm barking up.