My guess is, that Apple did not invent this to prevent others from implementing it or have something proprietary, but just because the iPod Shuffle used the same connector for Headphones and USB (see page 8 in [1]), so they somehow had to ensure, what type of cable is connected to prevent damage to the iPod.

Another interesting fact:

The iPod classic 2009 does support some of the features (play/pause, next, previous), but lacks support for fast forward and rewind (click + hold, 2 clicks + hold).

1: https://cdsassets.apple.com/live/6GJYWVAV/user/locale/de-de/...