Ipod Composite AV Cable Firmware Compatibility:

I discovered that the generic ipod composite cable, multipin connector with 1/8" audio and usb power breakout connections, is not compatible with my iphone. When plugged in my phone says charging is not supported with this accessory.

The more I search online I find information about cable compatibility being based on firmware version. Can someone please explain to me why a cable charges an older device with an older firmware version but not the most up to date OS?

Thanks for the help,

-P