The reasoning for 15/20 amp receptacles on 15/20 circuits is this. 15a and 20a receptacles have different pin configurations. A 20a receptacle will have one slot that is turned sideways or T shaped to allow a 20amp plug to be used. A 15amp receptacle on a 20 amp circuit will not overload the circuit.
AFCI Electrical Outlets - AFCI protection is much like a GFCI outlet, but it protects against an entirely different potential danger. Sometimes, certain types of electrical appliances will be used to convert electricity into heat. Sometimes, these devices will also cause heating where the device plugs into the wall.