[Joe Wicked]

Good to point out Ron, I was talking about the filler tube. The fuel nozzle does not normally touch the cap, so the filler tube is what is important. Plastic does hold a charge if left alone, but if it is making contact to the filler tube, which is then in chain making contact to the car chassis, then it will not be able to build a different charge.

As far as the Mercedes, it may well be an isolated, ESD (ElectroStatic Discharge) coating or isolator that would completely isolate the filler and the rest of the car. It would also prevent a sudden discharge. Standard Plastics and Rubber will not work. It would have to be ESD specific. These have a Very High resistance and many will read this as open, but it is not. These materials are used in Electronics Manufacture and Repair all the time. It will cause a very slow discharge that will not produce an arc. On a higher end luxury automobile, I would not be surprised that they incorporated something like that into the design.

Edit: The purpose of the ESD materials is to protect sensitive electronics, but the same principals apply, so it would be a good application.