My experience is different. I had two 10 rd mags for my g19 for the past 10 yrs. One was kept fully loaded at all times, I switched every yr or so. Those mags were probably only used 10 times or so at the range, so they were not cycled too much. Now the last round in both mags ftf's.
If you load a new mag and leave it there for 10 yrs maybe its fine, but any kind of cycling and you're better of replacing springs every 5 yrs or so.