In at least some incidents, it was impossible to change into neutral(owing to some electronic failsafe) and not at all obvious how to switch the ignition off. Non-obvious is bad bad bad when your throttle is suddenly stuck wide open.
[1](http://www.caranddriver.com/features/09q4/how_to_deal_with_u...)
In my car there's nothing preventing you from completely removing the key while the car is in drive (this actually screwed me once when I parked on a hill and forgot to shift to park). Is this unusual?
(I've been told that holding the power button for several seconds, just like one would a crashed computer, will force a shutdown; can't verify that though.)