It happens, whether that was the case with Britney or not. A friend of my Brother, whose kid nose dived off the bed. They had thought he was old enough to do without the side rails. Later that day the kid playing with one of those plastic Basketball Goals that are adjustable, ram into the backboard scrapping his face just under one of his eyes.
The incidents you described do indeed happen.
But a re4sponsible parent does not allow their child to sit in a highchair without being strapped in.
I always strap my daughter in and there is a pad underneath her highchair which is much softer than our hardwood floor.
And I hope you'll agree that it is pretty darn rare for kids to sustain skull fractures even when they fall out of bed or run into backboards.