Nal,
It keeps coming from the fact that your "proven" statement is far from being a total guarantee of each & every spring's performance in every gun that has a spring.
It may well be a general rule, but it is not an absolute.
Metallurgy, age, load, and spring type are all factors.
I won't waste your time or mine debating the issue, but I will say that while the often-used example of WWII 1911 mags left loaded for 60 years that function fine may be perfectly true, I'll also say that the Glock mag springs in my 17 back when I was carrying one fully loaded 24/7 WOULD & DID take a set within two years.
That gun was not fired all that much, but the only malfunction it ever (then or in over 20 years of possession) exhibited was a factory mag spring that didn't have enough soup left at a department qualifier to avoid a follower jam with several rounds left in the mag. The jam left the round column sitting with the top round stuck too low for the slide to pick up. Mag fully seated & not dirty.
Our department armorer made it a regular practice each year during the annual teardown inspection to replace mag springs that had shortened to a certain point.
It was not just my mags, and it was a known occurance routinely handled.
My comment about shotguns resting with hammers down to avoid longterm compression simply ommits taking a chance on springs weakening.
You're free to do whatever you wish with your own guns.
Denis
