It's not even that clever, really. The camera power rail must be physically close to the camera, so it's trivial to hang an LED off it. A device manufacturer has to go out of their way to make it so the LED and camera function are independent, and I'm sure many do, for the worst reasons you can possibly think of.
Nest cameras used to have a user toggle to enable/disable the camera LED; not the worst reason I can think of.
It's more a testament to how little most companies care. The solution is simple and yet most products are defective.