I understand your examples and feelings behind it.
However, contrary to (I guess popular) belief, with how things are machined and in spec to within thousands of an inch, a 'break in' time would/should occur within the first few miles.
Longevity wise, sure it's a good idea to not hammer the ever living **** out of a new vehicle and to rather take it easy for a while.
It may be my luck (although I'm doubting it), but coming from a person who bolted a Vortec to a new Mach-1 with under 1,ooo miles and seeing 0 problems, I'll debate my own statement.
Not debating your statement on how things need to be worn in, per-say. However, would it mean that a NASCAR has performance gains as a race goes on? Or perhaps a top-fuel car (which has its engine rebuilt after every pass) see improvements as well?
Sure a person's car may seem different or 'come more alive' after *** miles, but I'm willing to bet if a car hits the rollers at 100 miles, then again at 2000 miles, if there are any changes, they won't be substantial or even noticeable...except on the dyno graph.