I believe it has to do with todays machining processes vs yesterdays. The finish they can leave now is nearly the same as a "broken-in" engine, so not much breaking in happening right out of the gate anymore like there used to be. And, they are also reducing the number of things that break-in. I don't think anybody makes flat tappet camshafts anymore, they are all roller lifter or OHC roller follower. That really only leaves the rings left, and with how they can leave cylinder bore finishes now and sprayed on/static applied ring coatings, it is probably mated during the first 3 seconds of engine run time in the plant, before it leaves the factory door. For anybody that thinks their new car has not been run at wide open throttle, your wrong. When a vehicle leaves an assembly plant, it is put on a "rolls" dyno rollers where all functions are checked, including wide open throttle acceleration rate, which indicates engine developed power for proper operation, in addition to all lights, switches, radios, wipers, turn signals, headlight aiming, etc.....