Break in time for new engine

Great post, this question has puzzled me for a long time.
When the automakers build an engine there is really no break in period like all the discussions above, at the auto factory the engine is assembled installed in a new vehicle sold and someone drives the car, you never hear people talking about their engine break in period, although if you read the owners manual there is a blurb about the first few thousand miles.
Enjoyed all these post