I think I remember we discussed this before? In a 32-bit game you get 4GB of memory, which should be all AH needs. I think they load everything into memory and they really don't need more. If that is still true, then the only benefit a 64-bit version would provide would be concerning artificial intelligence which we don't have. Ah does have a limited AI (I think), but even that doesn't need a 64-bit version. In AH I would expect a 64-bit version might be needed if you wanted AI that could learn and modify its actions.
Now, graphics cards have a completely different system for bit-widths (I think 256-bit actually). That's why a GPU can do textures, vertices, 3D audio, PhysX, and so on all at the same time.