Since the nominal 15 or 20amp protection does not protect against using a lamp cord that is not rated for the load it is carrying, that point seems to be moot.
TheKid:
What the 15 amp receptacle configuration does for you is to protect the circuit from connection of a (properly wired) appliance of greater than 15 amps being connected, since the plug doesn't fit. So if you have a circuit wired at 20 amps and limit connection to 15 amps, there shouldn't be a problem.
The T-slot in the 20 amp receptacle allows you to plug in your 1 amp appliance with a 15 amp plug into either receptacle.
