Making it on the App store with games is extremely hard. I have 3 friends who each developed a mobile game and made no money, basically the games serve as portfolio for future work. I don't think the quality is the issue with what my friends produced:

http://www.whitebat.co.uk/fruitfrenzy/

http://gamewhizzes.com/

http://ludimate.com/x-rainbow/index.php

Most likely marketing failures.

That being said, I am working on one myself and have all the hopes that any indie has.