*edit by OP* springs do get weaker, but is that a problem? check out a box of surplus glock mags and compare the spring tension to new mags. seems to be a big difference, a lot more than lot to lot manufacturing variation would account for. Even in the one box of surplus mags, one can find some springs much stronger and some much weaker. There's a reason vendors sell spare mag springs. We should think about more than just springs. sure, we can cite WWI and WWII mags still shooting fine BUT we can cite multiple examples of mag failure. If someone can't, they haven't been shooting much. I have seen a half dozen GLOCK mags loaded by LEO and carried in the spare mag pouch for years that swelled slightly, making them stiff in the mag well for insertion and ejection. They functioned fine but stiff. I have seen hundreds of mags rusted into non-functional condition. I have seen spiders taking up residence in mags. Think about sand, dirt, mold, rat piss, etc. If someone isn't checking the mag, then maybe they're not checking the bore, either.