I'm pretty sure cars do not have a regulated bus. You pretty much get raw battery power, which means it can be:
- really low when cranking (<9V)
- negative if someone hooked up the battery backwards
-
24V if a helpful tow truck operator wants to give you a REALLY good boost and uses two batteries in series
- temporary >120V load dump if the battery becomes disconnected from the alternator while charging
Cars are definitely an environment for "rugged" electronics 