I bought a 2012 4Runner last year and was mildly concerned about the lack of a locking gas cap or cover. I was reassured that "no one siphons gas today" or "thinks about putting a foreign substance in a gas tank." Tonight I visited our local gym and parked with about 20 other vehicles under lights and in plain view of a security cameras. After spending about an hour in the gym, I returned to find the fuel door open and gas cap dangling. While it appears no gas was siphoned, I have no idea if they put something in the tank, which is a plausible concern for a $40,000+ investment. The only other car in the parking lot with the same issue was a newer model Ford pick-up, also with no locking fuel door or gas cap. Any car with a locking fuel door or gas cap was untouched.
Here's some additional data on the subject. Listed below is my history of car ownership, whether it had a secured or unsecured gas cap\door, and stolen gas or compromised gas caps\doors:
No locking gas cap or door and number of times the gas cap or door was removed and\or gas stolen:
'66 Dodge Coronet - 2
'67 Cadillac Cp Deville - 1
'88 Mitsubishi Mighty Max - 2
'12 Toyota 4Runner - 1
Locking gas cap or door and number of times the gas cap or door was removed and\or gas stolen:
'76 Honda Accord - 0
'80 Honda Accord - 0
'80 Toyota Celica - 0
'96 Honda Accord - 0
'99 Honda Accord - 0
'00 Toyota Celica - 0
'01 Hyundai Santa Fe - 0
'02 Toyota 4Runner - 0
'05 Honda Odyssey - 0
Feel free to make the call, but in my experience the evidence seems to speak for itself. While some may consider it minor, the peace of mind for some owners and the sufficient deterrent for most criminals appears to warrant keeping a lockable fuel door. At a minimum, it would be nice for Toyota to offer an OEM option for a locking fuel cap. For now, I'll be looking into aftermarket options.