Its just that now it has had about 7 major iterations (not counting 'S' models etc.), it is really in the 'consolidation' stage of the battle. The storming of the castle is done, now the army is battening down for the long siege and the door to door skirmishing, slowly moving the front forward.
The only way Apple (or any manufacturer) can claim another 'revolutionary' step is if they come out with a foldable display screen, or a 30 day battery life or similar.
It's a shame. The only smartphones I've ever had have been iPhones, and I don't want that to change. But I'm not seeing much reason lately to believe that Apple can continue going from strength to strength.
I would agree that their newest changes aren't revolutionary in my mind and are more iterative, just spec bumps and features added, but everyone is still taking their cues from Apple when it comes to functionality.
I would argue that some of the S models are more significant iterations than the main numbered ones. Siri shipped with the 4s, the Appstore shipped with the 3G (IMO it's fair to call the 3G and 3GS "S models" of the original).
I'd say they made some pretty major strides and set the standard for what a smartphone would look like for the years to come, and by and large all phones still follow the iPhones original path. Sure, different phones and different Android releases now do stuff different and sometimes better than iOS, but for the most part, it's all just following the iPhone.
[1] http://www.theatlantic.com/technology/archive/2013/12/the-da...