It's all part of the USB standard, there can be different "levels" of chargers. If I'm just travelling with my phone, I don't want to have to bring a 240W charger. It would be way too expensive and also too big/heavy. The good thing is, if you have to bring a big charger anyway, you can also use it to charge your phone or your headphones. That's what the standard is all about.
yes - this is exactly what I mean. They've legislated the interface but not the standard.
It's all part of the USB standard, there can be different "levels" of chargers. If I'm just travelling with my phone, I don't want to have to bring a 240W charger. It would be way too expensive and also too big/heavy. The good thing is, if you have to bring a big charger anyway, you can also use it to charge your phone or your headphones. That's what the standard is all about.