I don't see that the design of other popular SmartPhones has radically changed much in the last year or so either. We're at the point where the SmartPhone is pretty much a finished product. There will be spec bumps, software improvements, and some small arbitrary design changes but it can't get much bigger or smaller, it can't get much thinner before holding the device in your hands becomes difficult, and it's unlikely it will get radically lighter due to the weight of the battery. What else is left? We're really talking about very small changes that probably don't have much, if any, impact on the market. The 14 month old iPhone 4 is still the single best selling model of SmartPhone with the 26 month old 3GS coming in at number two.
What Apple does need is a competitor to the 4-4.5" Android devices. According to the rumors that's what the iPhone 5 was supposed to be. If they have to go another 12 months without a competitor they will probably continue to lose more marketshare. If you look at the sales of Android phones they are almost all 4-4.5" devices so you could say it's the fastest growing segment of the SmartPhone market. Hard to say if people are buying them because they are increasingly the only option for an Android phone or if they prefer the bigger size. Either way it's probably safe to say a significant chunk of the SmartPhone market wants the bigger size.
What Apple does need is a competitor to the 4-4.5" Android devices. According to the rumors that's what the iPhone 5 was supposed to be. If they have to go another 12 months without a competitor they will probably continue to lose more marketshare. If you look at the sales of Android phones they are almost all 4-4.5" devices so you could say it's the fastest growing segment of the SmartPhone market. Hard to say if people are buying them because they are increasingly the only option for an Android phone or if they prefer the bigger size. Either way it's probably safe to say a significant chunk of the SmartPhone market wants the bigger size.