Being a store exclusive is not surprising... it does make it an expensive extra if you don't have an expensive home theatre system that would even notice the difference of the 4K UHD.
That's interesting... I doubt that it would be a different cut to the movie (before it was modified to be reclassified PG here), as it is likely due to the bonus features (including the more violent cut scenes) as the reason the bluray & 4K versions have an M rating (the DVDs only have one bonus features, or none at all).
- It appears all 4K UHD and Blu-rays are the version rated M, while all DVDs are the version rated PG (both the regular cover and the Big W exclusive).