It's a context thing. The point of adding the author as reviewer is to keep them in the loop, show an alternative solution and discuss which way to go. Also to learn why the did it the copy/paste route in the first place - it might be carefully reasoned, it might be a rush job, they might not know any alternatives.
Also to put the conversation on record somewhere so that if someone comes later with the same complaint they can see why the code was written like that.
