Apple's next iPhone: 4-inch display; 12.5% more productivity

Does this start to lead to fragmentation? Enough that developers will have to start thinking about different models when building their UI?

I personally still run IOS 4 on my original iPad as well. A number of developers / apps require IOS 5 (ex. iHeartRadio) that I can't use.

It isn't as fragmented as Android but is the IOS ecosystem reaching critical mass where developers will have to build multi-display optimization code and once you've done it how much incremental work is it go from supporting 2 resolutions to supporting N resolutions?