I agree-- magazine is not just something to hold ammo-it is part of a firearm. you can shoot and drop a mag without having to "train doing the same thing because of muscle memory" in an emergency without having to worry about dirt or whatever in your mag, damage, etc. (the whole uncertainty factor-how many times have we found something out after the fact that affects reliability etc.).
not to mention you have to shoot a few mags just to make sure they function reliably--granted it is practice, but that money could be invested in mags or other needed gear/guns --to be honest I reload and cannot afford to test all my mags (I have that many)
My dad used to tell me "take care of your tools they will take care of you" glock may be able to handle abuse, buried, thrown, dragged behind a truck in a rocky desert--but you really want to take a chance and have it click when you need it to go BANG?