WOW, we have really strayed from the OP’s topic with this.
It’s good to have guys here interested enough to turn it inside out though.
I guess this could go around and around depending on the persons point of view and how they interpret the NEC.
I would agree about the rating of receptacles except that when you have more than one single receptacle, such as a duplex, which counts as two receptacles, 210.21[B],[3] allows the use of 15A receptacles on a 20A circuit with a maximum cord and plug connected load of 16A, as per Table 210[B,[2]
That would exceed the 15A receptacles 80%, 12A rating even when used as a single receptacle as per 210.21[B],[1] and is also above the 100% maximum rating of the receptacle itself, which appears to be what 210.21[B],[2] is supposed to prevent and is apparently it’s whole reason for being. This in itself would indicate that receptacles must be designed for use at 100% of their rated capacity.
The 80% limitation in Table 210.21[B],[2] is on the receptacles themselves, not the branch circuit. It doesn’t differentiate between continuous or non-continuous use. It only allows you to use the receptacle to the maximum cord and plug connected rating of Table 210.21[B],[2] with no exception except for receptacles for arc welders, and electric discharge lighting.
The guys on Mike Holt’s site determined that listed receptacles are rated for 100% of their capacity.
That would bring us around full circle.
Since receptacles are rated for 100% of their capacity, there should be no hazard in allowing them to be used at 100% of their rating for non-continuous loads and 80% for continuous. Others have also made the determination that the 90 degree C rated 15A and 20A branch circuit conductors we use are already rated for 125% for continuous loads per 310.16, being 25A for #12, and 25A and for #14. They are protected at 80% of the max conductor rating at 60 degree C, that being 20A for #12 and 15A for #14 with 40 Degree C rated circuit breakers rated for use at 100% of their capacity.
Anyway, I still think it’s time to modify Table 210.21[B][2].
) Too many possibilities are out there that can be used on GP recepts. This is why there are several limitiations on recepts and their circuits. If a recept is installed for the a specific application, just like everything else, it has to be sized accordingly. 
