I think it's something like 10 rookie defensemen in the last 10 years have hit 40 or more points. Expecting it is a very tall order and sets people up for some disappointment.
Again, as I said in the Barrie thread, not to take anything away from his playoff performance, but it was only 10 games. He's never played a full 82-game season before. I'd say that, like most rookies, he's bound to hit a wall at some point.
His first season, I think 30 points is a reasonable AND high expectation for him, anything else is obviously great, but I do worry about unnecessarily high expectations on him, especially as teams will know to gameplan for him, so it will be up to him to adjust accordingly.