Ive talks about this. The point is that an indicator should be invisible when there isn't anything to indicate. Otherwise, it's just another tiny distraction.
..in Gary Hustwit's documentary "Objectified", for those interested in exposure to more sweet, reality-distorting Ive radiation. Recommended viewing.
That interview for sure shows passion and obsession for details. It gives an impression that Ive is one of the greatest industrial designers of our time partly because his obsession and understanding of manufacturing processes. He knows the limitations and possibilities of his tools.