It's probably too early to tell regarding this release.
Was it originally listed as 3D and then changed? Even if it was, it'll be because Zavvi probably assumed it would include the 3D disc, but then covered themselves by removing it in the listing. While Disney are known for offering bonus discs to various retailers, I can't remember the last time the 3D version was an exclusive to a specific retailer, and surely with Zavvi's relationship with Disney, if anyone was going to get a 3D exclusive it would be them.
Every Disney steelbook in recent memory has included the 3D disc (where applicable), Thor: The Dark World, Captain America: The Winter Soldier, Guardian of the Galaxy, Avengers: Age of Ultron, Ant-Man, The Lion King, Big Hero 6, Inside Out and so on. Even their Marvel re-releases had them. I can't see any reason why The Force Awakens will be any different.
People seem to be getting themselves into a state over a release that's still (at least) 4 months away, talking of cancellations and wanting all the facts now. The information will be available in due course and there'll be plenty of time to decide which version to buy. Every country in the world (more or less) will be getting a steelbook for The Force Awakens and I imagine there'll be a few variations to choose from.
