#1. Many people have an override switch for their ACC. So on short drives, they switch it off so when you start the car, your startup/shutdown controller or computer never gets the response that the car is on.
#2 Standby/hibernate DECREASES boot times. Again, a lot of people use a startup/shutdown controller which dictates what happens when the engine turns off.
#3 Their carputers are very much slimmed down in terms of computing capacity. It's just like if you have an aftermarket HU. The functions are readily available because it's only starting certain things. Many people have acheived fast boot times by slimming down what is starting and what takes priority.