i think you hit the nail on the head sequoiasoon. i remember my mother's camry having a "valet" mode where the correct master key would be used and if you turned the lock from the outside the opposite way it would lock the lock and the "valet" key would only work on the ignition. the difference in keys is the master key comes to what looks like an arrow head point, and the valet key comes to what looks like a stepped drillbit. i wish i saw this before i moved my car because i do have my spare door key in the car and could take pics of the two.
if you need a spare master key i'm not sure if your dealership offers the service, but here in hawaii as long as the car was purchased from the toyota dealer here you can go there with the VIN and they will cut you a new key. just have to show proof of ownership. i got new keys for my car because i was tired of the "spares" i had which would work one way, but not the other way, then wound up messing up my ignition so my car wouldn't start.
*edit*
just realized i have my wife's spare key in my pocket too. here's the pics with the difference.