Just to put your minds at ease, cars have power assisted steering, not power steering - semantics, but the difference is that you don't lose control when the PAS is off, it is just heavier as there is a direct mechanical link (dump trucks, fork lifts and so on use hydraulic steering with no direct link, so are not fail safe). Likewise brakes, whether it be through vacuum operated servo boosters or electrically powered brakes. Parking brakes, however, are a potential problem, now that premium brands are using electronic rather than mechanical systems. Most require the switch to be operated for several seconds before they will function with the vehicle in motion, but with the ignition off, who knows? But, pretty stupid advice all the same.