I suspect the thinking is:
  • The battery has to have sufficient capacity to last an entire 12-hour workday.
  • Users always plug the phone in at home each evening.
  • Making the battery/phone any larger than necessary for the above just adds bulk and weight, making it less convenient to tuck into a clutch-purse or pocket.

Or something like that. But mostly, I suspect Apple just wants to be able to make more moollah by forcing earbud makers to buy/license yet another proprietary interface.

Cheers