The problem I have with the "water hose diameter requirement for the sprinkler" analogy is that the sprinkler company is specifying a requirement for their sprinkler to work properly. A requirement that they’ve tested. Kind of like "use high octane fuel" for a performance car (and why using it in a car that doesn’t call for it is a waste). Still not a great analogy because it doesn’t take into consideration other parameters like your initial water pressure but whatever...
To make the comparison to speakers, do speaker companies specify the engineering requirements of the cable to make their speakers work properly? And how can they do that for some cables when the cable manufacturer keeps their "sauce" secret?
Is there some cable spec that the speaker designer is engineering into their product so that the result is what the engineer is shooting for?
The Magnepan 1.7i manual just says it supports cables up to 10AWG. I know the Vandersteen manual is way more specific on what cables to use.
The wires INSIDE the components (whatever quality they are) are there based on the engineer’s choice (balancing performance, marketing, and cost) so that wire is in those components purposefully.
If the manual says use at least 12 AWG, that’s probably the right route to take. Are there any speaker manuals that call for "use only oxygen free copper" or "use Audio Quest cables for best results"? They would if there was a marketing partnership!
Personally, I fall on the "buy a thick cable that looks nice but other than that, it’s not going to matter much" camp. But if the manual for a speaker said "use X gauge" I probably would.