I have herd some crazy things on this subject in the past. It is easy to confuse switches with receptacles here. Switches, the rating is for the device, with receptacles its the face configureation as well as the feed through capacity. All 15A. residential receptacles are 20A. feed through. I have checked this.
I beleive there should be a code change that 20A. face configuration receptacles should only be allowed as a single device circuit as anything that could use that config such as a copier, will be running neer 80% the circuit capacity rendering the rest of he circuit useless and causing an overload hazard. Besides, even in spec grade situations the 15A. spec grade receptacles are cheaper.