Marching into the brave new world of silos, a car is an easy addition to Apple platform, while GM would need to build a platform to add to their cars.
In modern cars where nearly everything is computer-controlled and un-serviceable by the end user, safety is pretty much guaranteed, and fuel economy is average.. what other choices are there? It's just as plausible that someone would choose a car based on built-in entertainment options as that they'd do so based on color scheme.
who said entertainment system? Design is among, if not the, main aspects when people decide on tech choice. With cars being electric - simple commoditized drivetrain - design will become even more important.
i think electric cars for some segment like "Millenial urbanites" would be a market where Porsche and Mercedes don't have any starting advantage in car design over Apple as all their established design themes of high power/dynamics, masculinity, posh-ness, etc... wouldn't resonate that much there.