would put a magnet in there just to keep the lid down so it would not flip up and hit me in the nuts. If I were gonna steal gas from one of these bikes I would pull the hose and tun the petcock.
I think its mor to keep people from putting crap (sugar,sand,rocks) IN the Tank moreso than taking gas out.... but thats what an in lnie fuel filter is for
I'm sure theres some A-hole out there that does that sort of things,