Even today - a USB 2 port might not have enough juice to power your hard drive, so we're already in a state of "non standardization."
I look very, very forward to the day when a USB C port means that I have a very strong chance of getting 15 watts for my tablet/phone from any vendor - and the sooner apple adopts USB C for their iphones, the better.
It even happens at the cable level. I've had a couple of devices (Galaxy S3, Mophie) that required me to the use the proper higher-quality cable, despite being standard micro USB.
If i recall correctly, that's because the basic signaling for USB charging is resistance based. Too high a resistance on the wire, and it may heat up (even melt the plastic wrapping) if they try to draw more than the default 500mA USB amount.
I believe that higher currents are negotiated with digital signalling. Does that allow for the two ends talk to each other to determine the performance of a cable between them? The Apple lightning cables themselves include a chip.
Anyway, an interesting thing about USB C (and maybe 3.0, too) is that it can also negotiate 12 or 20 volts and even up to 5 amps. For the same wattage, a higher voltage will heat the cable less.
If the data pins are shorted facing the device (so that the device detects its own outgoing signal on the incoming pin) it will consider the port a dumb charger port and attempt to charge from it based on the cable quality.
If there is a proper port response, and the port claim to be a charging port, the device can ask for more than 500mA in increments of 100mA. There will be limitations depending on there being ongoing data traffic or not.
USB 3 cables identify their current capacity through resistive values on the ID pin. Voltage negotiation is also permitted for USB 2 although I doubt it's used much outside of niche products designed to work together.
I look very, very forward to the day when a USB C port means that I have a very strong chance of getting 15 watts for my tablet/phone from any vendor - and the sooner apple adopts USB C for their iphones, the better.