It may be due to some analysis as well. Having done a few failure modes and effects analysis in my time, its common for engineers to identify such modes, perhaps do a bit of testing and revise a design or establish operational guidelines to prevent an actual situation from arising. The ability of an HF transmission to cause a spark in a nearby structure may have been something they observed in a lab.
Sometimes we don't wait for things to blow up before we fix them
Wonderful theory.
Q: How old are aircraft? How old is HF as used in aircraft and what was the wattage of the first systems?
Now like I said before I could understand this in a 742 with the couplers and ant in the wingtips but the same policy is followed on the MD-11 with couplers and ant in the tail under the #2 inlet... There is no nearby structure that a spark could ignite fuel from. I claim wives tail based on an experience of a Darwin award recipient many years ago.