The ascension of Nintendo was one of the great triumphs of entertainment marketing. In just five years the Japanese company transformed a moribund U.S. video-game market into a $4 billion industry and created a video character, Mario, whose popularity rivals that of Mickey Mouse. But fads are subject to the law of gravity. Even as it was announcing record earnings for 1990, the world's largest computer-game maker confirmed last week what retailers have been saying for months: the Nintendo market has gone into a spin.
Shipments of Nintendo's basic game-playing unit, which peaked at 9 million in 1989, dropped to 7.2...