Someone once told me that the static charge generated by fuel flowing through a refuel hose was greater for kero based (jet engine) fuels than for gasoline based (piston engine) types.
I can't back this up by hard evidence because I have forgotten who it was; however if true it could explain why cars don't need a bonding lead at the filling station.
BTW, every wheeled helicopter I have flown has been fitted with u/c static grounding leads that touch the earth first.
ShyT