The steering can only lock if the key is removed. Cutting ignition power only stops the engine it cannot lock the column. A manual transmission car will still have power steering assistance until it the car stops moving unless the driver pushes the clutch in. Even worst case the steering reverts to manual steer anyway which just needs more muscle. Car steering and brakes have various failsafes to stop catastrphic failures.

Likewise, cutting the engine while driving will only eliminate vacuum in the brake booster, the master cylinder is still directly connected to the pedal, it's failsafe. The driver just has to push a bit harder.

I can understand that people like to embellish the story of their "near death" experience when the car cuts out, but in reality they just need to harden up and get on with the job of driving the car as best they can in an emergency instead of panicking.