with the pushbutton start on new cars, you have to make an effort to leave them there, most people never take the key out of their pocket (or purse for most women) soooo . . . . . .
and even my truck which still has a 'key' you have to turn it to shut off the car, pretty natural motion to turn it off and pull the key out
as a side note my wife has a bad habit of not locking the car (in the driveway) when she needs to get something from the trunk because the keys are always buried in her purse and she wont make a trip back out to the car