<. You are gradually managing to teach me the fundamentals of electric circuits under the hood (Business Admin grad here), and I confess it's fascinating and gratifying to understand. >
Yes.... We have ID Nick-Names here for most posters , and yours is
"Car Learner"...so , seems approriate that you mention that....
.......
Anyway, you have the basics correct... a direct unfused short to ground will effect the systems voltage back to the battery source, whereas the aux fan circuits would blow the feed fuse if it incurred a short and the source would never know the difference. Itwould simply see a 20A draw on a 15 A protected circuit before that fuse blew...and a 20A draw on a system is nothing...the source simply sees that as an accessory draw..like you turned something on.
Whereas , a direct unprotected/unfused short can draw MANY ,MANY AMPS...
So many, that the wires burn up in a flash. Ever put a wire across a battery ???? ............ "POW"