Full of poop, IMO.
I've always heard (from reliable sources, such as mechanical engineers) that springs are primarily weakened by compress/decompress cycles, not time under compressed load, as long as the design limits of the spring have net been exceeded (such as over-compressing or bending/stretching them). I've personally fired ammo out of magazines that were loaded and left full for over 20 years (AR-15 and Mini-14), that functioned fine when finally used, and those same mags continued to function properly for many more years. Heck, I'm probably still using the AR mag, but I'd never be able to tell which one it is. I also have Glock mags with all original parts that were still perking along with no problems after 20+ years, some of which had been loaded for more than a year at a stretch; and then I sold them to folks in states that still had AWB-style magazine bans in place, and they're STILL using them.
When you find a reference to "replacing magazine springs yearly", you might be surprised at how many times this has originated with a company that sells replacement springs. I've seen it a lot in online sources, especially ones aimed at Law Enforcement or concealed carry folks, usually using the old "How much is your life worth?" or similar statements to sell replacement springs.
I'll see if I can find some sources for you to review on the subject.
EDIT: Try this article:
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)