The rod is designed to keep the top of the bottom section of the case together where the zorro cards go. It does help a bit in keeping the case from warping and takes pressure off of the individual zorro card slot plates. So it does serve a purpose. Without it, some cards are more difficult to attach the slot screw to and put undue pressure on them as they are helping to hold the shape of the metal box together.
Again, not absolutely needed but nice. You could probably make your own by buying a threaded rod, coating the middle section in plastic shrink wrap or non-conducting material and using a threaded eyelet on the end attaching to the zorro backplate.
