Well, the size of the pins is never going to have anything to do with voltage. Voltage ratings are always a function of insulation, whether that is in the form of an air gap, some sort of dielectric material like wire insulation, even the dielectric properties of the material the connect your body is made of.

I'm going to read over this. Remember that there are plenty of very thin conductors that carry high voltages. The pin size only needs to be able to handle the amperage, as well as having reasonable properties against wear. In fact, one of the reasons that higher voltages are often used in a DC circuit, is to allow more power capacity with a given size of conductor. Look at Qualcomm with quickcharge 2 and 3. Your normal USB cable is good for roughly 2 amps, maybe a little bit more, so you can't increase the amperage beyond that, but you can drive up the voltage and just use a buck converter in the phone. That's also why those phones get so hot when they are charging.