Apple has plain and simply mastered the "less is more" philosophy. Same reason Google got where they are now from offering a website with nothing but a single text input in the center (rendering Altavista and all the huge crowded "portal" sites obsolete in a flash). Ubuntu changed the Linux landscape by being the first to offer a tightly integrated and stripped-down-to-the-essential software installation. Firefox made a huge splash when it originally was little more than a very simplistic frontend to the Mozilla monster suite. Ruby on Rails. And the list goes on. If you look at the huge successes of the recent time, this is a very common pattern.

It's not that simplicity alone is a winner, but simplicity allows to focus on your strengths and make them really shine. That's also why Maemo 5 has been so stripped down in many ways. Not everyone likes it or wants to admit the connection, but it's an immensely powerful paradigm.