Apple is doing well - amazingly well - with their iPhone sales. And they do a great job of giving the impression that they are the only player left, the only phone you'd want, etc. etc. But lest you think it's easy to get stay at the top, it was only four years ago that Motorola sold 46.1 million phones in one quarter. In Apple's best quarter so far, their most recent one, they sold 8.8 million iPhones.
It's hard work to get to the top spot in an industry. It's even harder to stay there.
An interesting side note - Motorola currently has 117 different models of phones that they currently sell. Apple has one (two if you count the fact that the previous generation iPhone is available for sale in most markets). That's the benefit of deciding on what you're going to do and focusing on it and doing it well.