This is a good point to bring up. I believe that spread spectrum clocking and DC-balanced line coding schemes on differential buses have allowed the rules to be

This is a good point to bring up. I believe that spread spectrum clocking and DC-balanced line coding schemes on differential buses have allowed the rules to be bent somewhat. However there is still an EMC issue present. It would be nice to have a metallized film or plated mesh to reduce the problem caused by glass and plastic. Old equipment used to have copper fingers on all seams and I don't see that as often anymore either.