In a piece on iMore.com, Rene Ritchie, seems to think that Apple is facing a challenge of keeping the iPhone fresh - and by extension - interested in the fruit themed smartphone.
"Thanks to Apple's tick-tock product cycle, where a new design is introduced one year, and that design is iteratively updated with new internals the next year, both of those problems -- consumer presumption and competitive counter-programming -- become amplified.
When the impression is that Apple will "only" release an S-class phone in any given year, consumers might be more interested in seeing what else is out there. They might be interested in seeing something different."I happen to like the iPhone 4/4S/5 form factor to that of the iPhone 3G/3GS. (The original iPhone is sort of a compromise design that I could live with, but I'm not excited about.) I've also said that if you read technology blogs like Smartphone Fanatics, we're not the target market for Apple. Or Samsung for that matter.
I have a lot of respect for Rene's work and I recommend that you read his 'The "iPhone 5S" Problem' article on iMore.