This one probably isn’t news at all, but I only recently heard of it, so I’m posting it.
Apparently, Apple requires that chargers for their devices use the data lines to signal charging power, and without using those lines, you don’t charge.
Apple requires a confidentiality agreement to get the resistor values, it seems.
Or, you know, you can break the damn thing open and measure the resistors. But still, you shouldn’t have to do that. Maybe to draw over 500 mA, yes – that makes perfect sense, as it’s over USB’s maximums, but not for the standard 500 mA.