Ever hear of "Fan death?" Korean urban legend has it that if you leave the fan running all night long it'll drain all the oxygen out of the room and kill you. No kiddin'.
Thus, adding a timer alleviates fear among superstitious folk and it's a power saving feature anyhow.
Whoops, missed the "I'm not saying..." It is a mystery, but yeah, it's probably due to "man, if it keeps them buying our products, we'll just sell it as 'power saving' and let the weirdos come to their own conclusion."
No, K9, the fan needs to stay on so you can keep the evil spirits at bay while asleep. For maximum effectiveness, attach a clove of garlic in front of the fan.