I didn't carefully read the articles I referenced earlier, and it appears neither of them applies.
While there doesn't seem to be anything directly prohibiting the oversize of a receptacle (and in some cases specifically allowing it), I don't understand how this doesn't violate 210.23 which supports my original argument(emphasis added):
In no case shall the load exceed the branch circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it is rated. A branch circuit supplying two or more outlets or receptacles shall supply on the loads specified according to its size as specified in 210.23(A) through (D) and as summarized in 210.24 and Table 210.24.
Certainly if a piece of equipment has a 30A cord-cap there is the real possibility it will draw more than 20A. If someone were to plug it into the available 30A receptacle, it would exceed the rating of the 20A breaker causing it to trip. This violates 210.23, correct?
Is it the responsibility of the person owning the equipment to ensure that a circuit is capable of handling the load they impose on it? Even if the receptacle on the circuit is designed for the rating of their equipment, and this receptacle is the only load served?
Or is it the responsibility of the installing electrician to ensure that using his installation as designed does not invariably creat a code violation?