The forthcoming iPhone 5S wil reportedly have the same screen size as the current iPhone 5. This will be a significant disappointment to some and potentially cause them to skip the update and wait for the iPhone 6, which is supposed to deliver a larger 4.8 inch screen. That could have a meaningful negative impact on iPhone 5S sales.
A recent survey from Retrevo shows that iPhone owners/buyers want a larger screen than the 5/5S has to offer:
The survey also showed that a significant percentage of would-be iPhone buyers have a "wait-and-see" attitude about buying their next iPhone. This is becoming a problem for Apple as media-fueled rumors of better hardware in the future cause people to delay purchases, unlike Android buyers apparently:
Despite the wait-and-see approach and yearning for a larger screen iPhone buyers are paradoxically much more loyal, according to the survey, than Android owners. This has been confirmed by other, previous surveys (e.g., ChangeWave) as well.