So because of developers... the iPhone can never change. That's crazy.
It can change and it has changed twice by going Retina and going taller. But it can not support multiple resolutions for an unlimited amount of time because of developers. For a short transition period interface designers have to deal with multiple resolution, until the old legacy resolution is phased out and everything is back to normal. Normal means there is only one resolution per category of iOS devices. One for iPhone, one for iPad. And one for some future device that isn't just a bigger phone or a smaller tablet, but a watch or a tv or something else.
This is more likely... same resolution on a larger screen.
It's the far better way of providing different screen sizes under iOS and therefore it's the only possibility for Apple to consider. Still they decided against it with the iPhone 5c. The decision against same resolution on a larger screen has already been made.
Let's face it... iOS is still the most desirable platform for developers. They will do whatever they have to do in order to build apps for the iPhone.
A day has only 24 hours and even Apple can't change that. The only way to increase productivity in programming is to reuse code and avoid doing work twice. iOS is a desirable development platform only because Apple makes the decisions necessary to achieve that. It is necessary that all iPhones return to having the same resolution.
Apple tells developers what to do... not the other way around.
That's not how it works. Apple figures out the best way to do something to achieve all goals and developers agree. It is not, I tell you what you have to do and you do it.
If Apple changes anything else in the future... developers will follow right along. It's their job. I might agree with you if ZERO phones larger than 4" have ever been purchased. But that's clearly not the case.
Their job is to make their customers happy. That could mean anything including abandoning the iOS platform altogether. Zero iPhones larger than 4" have ever been purchased and Apple customers are perfectly happy, naming the better app selection compared to Android as one of the main reasons. So better keep developers working on better apps, not the same apps in different sizes.
Some people like larger phones for various reasons.
People don't know what they like until you show it to them. Currently people like the iPad mini with Retina Display because all of their old iPad apps work fine on the same resolution screen. If you want to provide a slightly smaller or bigger form factor, that is the way how to do it.
Apple didn't want the 5c to be bigger and they think you are stupid for asking for it. Believe me, they have tested a bigger iPhone and the designers don't like it. In the voice of Steve Jobs: "They are crap. Who wants to have a brick in his pocket? We don't build mediocre products at Apple."
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Sorts of beer per country:
5 Luxemburg
7 Irland
11 Netherlands
15 Denmark
18 Italy
25 France
93 Great Britain
117 Belgium
5.000 - 6.000 Germany
10.000 - 15.000 Worldwide (including Germany)