If I remember correctly, although the fuse is aluminum, it is not made in the normal manner. Instead of making a skeleton of rings, stringers and longerons and then attaching the skin to it, the skins are formed to shape and then the structure is attached from the inside. Supposedly it makes a smooth, perfect skin instead of having the little bumps and depressions most airplanes have. I also seem to remember that it increases cabin volume a bit.