I thought it was done in the same manner as the old Pirate ships. So like the ends and middle were separate parts so they make the boats longer/shorter set to set.
I'm not keen on that tumbler either. I'd love to get my hands on that Two-Face set, and maybe some more goons from bricklink.GP: I wasn't too keen ont he Tumbler at all. The Joker van + Joker mini-fig is nice but I will stick with my Batmobile + Two-Face van. I got lucky with the Batmobile. There was one lonesome box of it at Big W.
In the Lego Batman game I noticed a few other sets crop up. The police vehicles were from last years sets and the Penguin Submarine is actually the totally awesome Aqua Raiders Submarine redone in black.
I want a Catwoman minifig. Off to bricklink I guess!
And it was good to see the city sets used in the game, makes sense when you think about it.