Hardware gets all the attention, but Apple's business depends on success in another area.Apple (AAPL -3.40%) sells some of the most admired products on the face of the planet. Its iPhone, a device in the 18th year of its lifecycle, is still so successful that it generated $44.6 billion in revenue in the third quarter (ended June 28). Add this to more items in the lineup, and it's no surprise this business is a consumer favorite.Without a doubt, hardware is important to Apple's success. But here's a number t ...