To me, Carl is just performing the song. Performing it VERY VERY well, mind you, but just performing it.
I agree. He hits the notes, no doubt about it, but Brian's slightly out of tune (at times), strained, rougher version makes the music come alive. Carl's, to me, is too...sterile? That might be the wrong word. It's very correct, and that might not be the way the song comes across best.