22-01-16, 11:37 AM
I think it's so you don't have to leave the key in the lock once you have opened the filler cap, you can just push to shut minus the key being there. I guess it's handy if you have other keys or objects on your keyring that might scratch the tank, but I don't expect most would have the equipment handy to mill out the required section. I've fitted an aftermarket non locking cap to mine as I have my bike garaged when I'm not using it and as it's black it goes better with the blue / black colour scheme than the OEM one.