One of the biggest jabs that detractors have when attacking the iPhone is its screen size, because some may say that bigger is always better. There are a number of reasons why that isn't really true, including personal preference, quality and efficiency. The first two reasons are pretty easy to grasp: some people may not like bigger screens for any number of reasons from limited pocket space, to the weight; and, some would prefer a higher resolution to a bigger screen. The last reason seems to be one that would tickle the obsessive side of Steve Jobs: the reach of your thumb.
Designer Dustin Curtis made a little mockup, which you can see on the right, showing how much screen real estate the average person's thumb can cover while using a phone with one hand. The basic idea is that a 3.5" screen is the perfect size for the average hand. Of course, the trouble with the word "average" is that there are plenty of people with much larger hands, and also smaller, so a wider range of screen sizes seems like a better approach. But, it also does show that bigger is certainly not always better. Additionally, "average" in this case likely means male and female, and most polls about screen size tend to have more males represented in the voting, which could explain the tendency for polls to show preferences towards larger screens. In fact, some may find it to be very annoying or unwieldy. People with smaller hands need to hold the entire phone deeper into the palm, which means closer to having your thumb at the side of the phone. Those of us with bigger hands, or better dexterity can hold the phone more on our fingers, and therefore will be able to reach a larger area of the screen.
There is also the other condition of the data, which is assuming you use the phone one-handed. Those with larger phones may have unconsciously begun using their phones two-handed in most scenarios because of just this reason. Still, given Steve Jobs' strive for what he saw as perfect, this seems like a reason that he would throw his weight behind in order to keep the iPhone screen size stable at 3.5". We can't say whether it's the right or wrong reason, but it certainly would explain it. The bigger question is whether this reasoning will hold with future iPhones or not.
source: Dustin Curtis
via The Next Web