It wasn't meant to be a direct analogy, just a simple example of how you get similar situations in general with electronic components, or really any kind of non-standalone component in most industries. Another example is fuses: a fuse rated at 20A will not immediately protect the downstream once load exceeds 20A, but rather, there will be a curve defined with respect to its nominal rating which defines how long it will take to burn out for any given current and ambient temperature. You may find at 20C, it will not even burn out at a continuous load of 25A, and at 30A it might take 2 hours. So if you're buying a fuse to protect a sensitive downstream circuit, you need to take that into account and use a fuse that's nominally smaller than the load you're running.

Essentially the "nominal" behaviour is not the actual behaviour, it's just a quick way of summarising the characteristics in a way that someone familiar with the class of item will be able to understand what they're buying. Another similar situation is timber sizing, where a 2" by 4" is actually 1.5" x 3.5".

In the case of electronic components, the actual behaviour will be either documented in a datasheet or just common knowledge in the industry. For example if you're buying a standard li-ion battery with no active circuitry, you'll often find the datasheet quite lacking in details because you are expected to just know the characteristics of the li-ion chemistry provided the basic parameters are provided.