The lack of big iPhones used to play well with developers of apps for them. All iPhones had small screens and most apps only needed one interface and display to fit them all. That changed with the recent release of large iPhones, and developers must adapt their apps to work better with them.
That's not an easy task, as iPhone apps must still support the millions of smaller phones out there. The careful design of apps for them goes out the window for the iPhone 6 and especially the iPhone 6 Plus. It's usually not best to simply scale up the app display to fit the bigger phones.
The iPhone 6 Plus is approaching the size of a small tablet, and it takes a careful design of the app interface to yield an optimal user experience. Apps that display information in a single column must be tweaked for the wider screen of the new iPhone without looking garish.
Many existing iPhone apps deal with landscape support as simply as possible. They don't support it.
Onscreen controls may need to be moved to a location that makes more sense on the bigger iPhones without compromising touch control. The controls need to be big enough for easy manipulation yet blend in well with the rest of the displayed elements.
All of this redesign must be done in a way that doesn't compromise how the app works on smaller iPhones. This is where developers must be pulling their hair out, as it's not easy to come up with a design that works well on all screen sizes.
Then there's the added difficulty of good landscape support, a must for the larger iPhones. The bigger displays cry out for using apps in landscape in addition to portrait. This adds a layer of complexity to the development effort.
Many existing iPhone apps deal with landscape support as simply as possible. They don't support it. While not always ideal, with smaller displays developers could get away with locking the app (and the user) into portrait use only.
When you look at an iPhone app that has good landscape support it is apparent why allowing use in all orientations is good for the user. The new CNN app is a great example of such an app. It displays information in an attractive single column (that is easy to control by touch) in portrait, and morphs into a two-column format when the iPhone is rotated to landscape.
It handles text, images, and video through it all, and is a versatile app that lets the user work the way they want. This is key, it's all about the user and not what's easiest to code.
This is a tough challenge and I appreciate the effort developers must put into getting it right. It's a juggling act to get apps to work best on small and large iPhones, and in both portrait and landscape. But it's an important effort that users will come to expect from them when they use the iPhone 6 and iPhone 6 Plus.
Many developers have long produced both an iPhone version in addition to an iPad version of their apps to appeal to a broader market. Or, they may have chosen to build a universal app that has code for both devices.
Unfortunately for app devs, as big as the iPhone 6 Plus may be, it's not big enough for most apps to just use the iPad display for the iPhone. What's ideal falls between the big iPad interface and the existing small iPhone UI. This is in effect a third tier of display support for devs who already have both iPhone and iPad versions.
App redesign is a lot of work, and the multiple requirements that large iPhones add to the mix are something that devs must address. Getting an app interface right for small and large iPhones is important as users are fickle. If they don't like the way a favorite iPhone app works on the new models, they'll move on to something else.