[Angrybird 12]

The thing is the Manufacturer's break in method is not just for the engine, it's also the entire drive line and brakes. transmissions and rear gears need time to "settle in" or find their proper set. Running the entire driveline hard over the first few hundred miles could put more wear and strain on those too. This is an area most people do not even think about.
So we are not just talking about engines here, but actually all of the mechanical parts of the car.