I can imagine one asking the same question with regard to the value of custom chips in phones, just prior to the appearance of the M7 through M9.
"Chipworks found that the M7 most likely is a NXP LPC1800 based microcontroller called LPC18A1. It uses an ARM Cortex-M3 core with a customised packaging and naming scheme indicating that it is for an Apple customized part"
Cell phones have power and size constraints that cars don't.