"So this is basically having a car, and leaving it unlocked, with the key in.'
In Australia (NSW) you don't even need to leave the key in! Leaving a car unlocked and unattended is already a crime in NSW and Victoria. There have been reports of police ticketing commuters at some station car parks because they don't want their windows broken so leave the car unlocked.
The mandarins just don't get it that those who are intent on doing naughty things will continue to do so irrespective of the presence of a law.