Not to doubt any of the good info presented so far..but... I must be the devil's advocate on this one, at least for a while.
Metellurgy aside, haven't we all had that Ruger MK II magazine that got easier to load as time went on? And don't make me mention Glock 10 round magazines..... That 10th round is a test of the modern hercules until a fully loaded magazine has sat around for a while and been shot and reloaded many a time.
Now, is that just me? Is it mass delusion? are we kidding ourselves about our mags getting easier to load?
so, the logically extension is that if they get easier to load over time, the springs must get weaker (or the magazine itself must be stretching.. yeah maybe that's it?) so couldn't the conceivable end result be that they get too weak to function reliably?
I too have one of those "found in the closet" WWII .45 mags that was loaded and worked fine (there were even two boxes of that old GI Hardball that worked fine after 40 years..I was young and foolish and I shot it all..), but I have percieved far too many springs as getting weaker to accept that they don't. My physics professor told me that a bowling ball and a feather should fall to the earth at the same rate.. well they don't.. unless the conditions are perfect and apparently I've had some imperfect magazines.
Seriously, I gotta go with my gut on this one, unless someone can get really convincing.