In the US ... here in California at least ... cars with manual transmission have an interlock where to start the car, you have to press the clutch.
In the UK ... and, I'll bet, the rest of the world ... they don't.
Very occasionally, you'll try to start the car, it'll be in gear, it'll lurch, you'll feel stupid, nearby people will mock you, and you'll get on with your life.
In the US, this doesn't happen. At least not so much.
In countries where automatic transmission is weird and unnatural and only for old and sick people (i.e not the USA), you just learn from the start to only ever start the car in neutral. You press the clutch, and wiggle the gear lever from side to side before you start the car. It's reflex.
It means that folk from the UK going to the US have literally no idea how to start a car until someone tells them.
It means that folk from the US going to the UK occasionally get unpleasantly surprised.
A little difference.