Bill,
The gas line bonding is part of an overall bonding philosophy as you described above. The FPN even suggests bonding ductwork. I actually called PECO one day to inquire about this and was told that they actually look for it to be done. Also, article 250-52(a) prohibits metal underground gas lines from being used as the grounding electrode. My brain is too tired to imagine the difference, as far as ramifications, between bonding to it and using it as an electrode. Maybe because complete isolation can't be assured, bonding is in order to minimize potential.
