Presumably there are other digital cameras that do not make a sound when taking a picture and these are the ones that are used. My gripe isn't with Apple but the legislation which I imagine hasn't really amounted to much.
my possibly wrong understanding isn't that this is law, but that consumers boycott phones without this "feature"
And that makes perfect sense. In an environment where the typical phone makes a noise, carrying a phone that takes photos silently is like wearing a sign around your neck that says "pervert".
The bad news for birdwatchers everywhere is that this trick doesn't work with binoculars.