Could this be an as-yet unannounced change to the way Air NZ sells domestic airfares?
When checking up on a future-dated Wellington to Auckland flight [Feb 2012], I noted that the "product type" was Seat + Bag, indicating that Air NZ's Seats to Suit product, previously limited to Tasman and Pacific flights may be coming to domestic flights.
Hey, maybe I'm way behind on this one and it has already been announced, but this is the first I have heard of it! Maybe it's just a website change and doesn't indicate a change to how the domestic product is sold. Anyway, a screenshot follows. As always, click on the image to get the best view.