A&Q about 350Z
Q:
i dont think they're all replaced, although im sure some are. the reason that the japanese rebuild their engines so often is that when the engine is rebuilt as to "new" condition you can legally (i believe) reset the odometer to 0, so that 30,000 miles before magically disappear at the cost of rebuilding an engine. for some reason unknown to me the japanese like to constantly reset the odometer, possibly for the purpose of selling it looking newer or just so they can tell themselves it's got a low mileage.
A:
It may have "low mileage" to them, but practically every other component of the car has 30,000+ miles
A:
Actually, what I was told (and I don't know if its true or not, but it seems reasonable) is that they replace their car engines so often because of strict emissions control laws. (So many people on a small group of islands....)