I can see why some people would think this is a pointless release, given all the comments about the German steelbooks available, but I hold a different perspective.
As someone who had a pretty difficult time obtaining the German version of Dark of the Moon for several months (multiple ebay auctions for standard 2D version slipped through my fingers and/or was never willing to pay the high prices). I finally contacted a member of another forum and bought the 3D version from them for 39 EUR shipped to me in the US.
The fact that people all over the world will get a second chance at the same steelbook for £14.99 could work in Zavvi's favor. I guess time will tell.
Also, Zavvi's one disc option will only serve to underscore the premium rank of the 3D + 2D + Special Features bonus disc. Even with this new release from Zavvi, the 3D offering will remain the King release of DotM. (I got the one from Germany, but the same can be said of all the other countries that released the premium 3D version of this, like Japan, Korea, etc...)