I'm still unconvinced either way.
I haven't noticed any lack of function in mags that I have kept loaded for months at a time.
BUT...
I have noticed that old-time flashlights that have had batteries stored for months at a time lose a LOT of spring tension and even when stocked with fresk batteries, they get intermittent contact and flickering due to weakened springs. It's probably attributable to crappy spring wire in the flashlights (haven't noticed this problem with maglites), but it does concern me.
In any case, almost every gun has springs that are somewhat pre-compressed (not to their full range, but compressed nonetheless). yet there are no shortage of century old firearms that function just fine with all original springs (including old integral magazine bolt action guns).
Even an unloaded mag's spring is under compression. If you are truly worried about a magazine spring taking a "set" you'd have to remove the floorplate and store it disassembled. Same goes for your AR's buffer tube.