Often the things that seem 'simple' to the end user involve significant internal complexity, masked by the software or hardware implementation of the electronics. The dark side is that quite often the process behind creating the solution is wrought from compromise and mis-steps. Sometimes it all works out nicely, sometimes it becomes a mess internally, with sub-optimal options going forwards.

In my view USB includes aspects from across the spectrum, the most visible of which may be the multitude of USB connector sizes and variations, especially on the 'B' end.

I did not mention in the prior description of USB charging that there is also a 'smart' negotiation protocol that is used when the charging device is a computer or similar. The host and end devices 'discuss' what is possible and work out what amount of power the device will take from the host. Apple uses this method when you plug an iPhone or iPad directly into a Mac, for example.

There is, of course, also a non-Apple protocol that does similar with Windows USB ports.