Debate with my wife about the role of the park button/brake

In the prius it doesn't really mater as the power-off engages the parking. However not every car is like that. I was just driving my dads 2006 LS430 which has keyless start, but you still do need to turn the ignition switch(no push button). I found myself repeatedly leaving the car in drive when I turned it off prompting the car to warn me to switch it to park. In most cars, as long as a parking brake is part of your procedure, the consequences are minimal. Chances are the shut-down procedure is going to become perfunctory in whatever car you drive regularly anyway. So a different car will cause you to develop different habits. But brake pedal, put in park, parking brake, ignition off will work in every car, so I see your point.