I do not agree that the engine chains do not need to be looked after, true they last a lot longer than belts but everything wears out. Tensioner's wear, oil pump chains wear, sprockets wear and only worrying when the chain flies out through the chain case cover is a bit too late. You may get lucky and the chain will only jump a tooth or two before you realize that something is wrong.
In an instant the engine can go into self destruct mode, pistons, valves etc are wrecked. At some point in the engines life the wear needs to be assessed and remedial action taken, 100 k. would seem the top end depending on usage.