I think the button push is there for the same reason people choose to have only the driver door unlock on one click and all doors with two. For security, unlocking the car should be a deliberate, not passive action. Poor analogy, but what if the ATM authenticated you via proximity?
If you're trying to get into the safety of your car, you don't want anyone near your car being able to get into your car. If you're loading the trunk, you don't want someone walking up and hopping in your car.
Most of us with time to argue about electric cars on the internet don't have to worry, but ask someone who lives or works in a rough neighborhood, or ask a woman how she holds her keys as she walks to her car in the dark.
Their threat model isn't my threat model, but i'm glad the mfrs are accommodating them.
That said, i would love if the electric cable lock released via proximity...