From what I can see, they have increased the lighting and lighting effects. The paint style is still there, but there is far more detail and likely more frames of animation. So that will explain the graphics portion.
The game is also said to be massively larger then the others at release, so that would account for the storage. I'm sure they also increased the physics, and other effects, which are resource hogs. Oh and they are using a new engine I'm sure too. They're tight with Epic, using the Unreal Engine in past releases if I recall. The newest engine is likely in play here too.
2K has done a great job optimizing games in the past and the BL series is a great example. If they're putting up seemingly crazy specs, it likely has a good reason and we will most likely enjoy the result.