Zelda games (esp. The Legend of Zelda, Link to the Past, Ocaraina of Time, and Windwaker) have all sold amazingly well- OOT has sold about 8 million copies. Nintendo will keep making Zelda because A: The fans love it, B: It's one of Nintendo's best-selling series, and C: They can
And, no Zelda games have been clones, I believe any Zelda fan can testify to that. The most similar things were the two Oracle games, but that was like Pokemon R/B (they're supposed to be alike).