"Fulfilling an existing need" seems somewhat misguided. In many cases the need is not always so obvious, especially at the conception stage. Its hard to imagine whether or not people will adopt something, at which point a need (previously unknown) is fulfilled. The iPad comes to mind off the bat as something many initially dismissed as not fulfilling any needs, only to meet runaway success when people figured out how to integrate it into their lives. What that means to me is that we should not always look to fulfilling existing needs, but to imagine new needs as things evolve. Its that kind of forward thinking that creates great products!