At a Marshall Rosenberg event I attended, he was asked about the unnatural speaking style. His reponse was that it was like "training wheels" for learning the process and, like you say, it doesn't sound like that once you learn to practice NVC natually.

And that may be, but my experience with various NVC teachers and practitioners is that they don't know the training wheel analogy and they do speak in an unnatural way for the most part.

Got a link for that YouTube lecture? (There are many.)