Small iPhone screen to keep iPad attractive
I don't know if this theory has been discussed many times before, but I just recently thought about it.
If I look at many people around me, most of them who have an iPhone, they have an iPhone AND an iPad. My girlfriend for instance used to do everything (browsing, emailing, etc) on her small 3,5" screen while sitting on the couch, instead of walking to her computer and it was a bad experience. When the iPad came out, she started using her iPhone only as a phone at home / work and when she's on the road she would just use the apps in a basic way (Facebook, Whatsapp, checking, mail, etc). In every other situation she would grab the iPad. I see this with many of my friends and colleagues. The iPhone became more of a phone and the iPad replaced a lot of online activity.
On the other hand we have the Android users: the people who have a Galaxy Note, Galaxy SII or SIII, Galaxy Nexus, HTC One X, Sensation, etc. They feel a lesser need to buy a tablet as the screen is already large enough for them and the difference with a tablet "feels" too small to justify a purchase (even though the Nexus 7 might change that). Especially the Galaxy Note is something that's perfectly in between. And the fun part is that mostly girls buy the Note around me, because they carry a purse which takes away "the big size" issue.
So I was thinking. Apple says (and they are right about this in my opinion) that 3,5" is the sweet spot for the average user with the average hand size. But the world has moved on (it's 2012 already) and people care a little less about the perfect ergonomics and prefer a larger size for a better content consumption experience. So even if all rumors are true, the next iPhone will get a 4" screen, with the same width, giving no advantage to reading websites and emails in portrait mode. And even then, 4" is very small for modern mobile phones.
My theory therefore is that Apple's reason to keep the iPhone small with a small screen size, is because they want the iPhone to stay a phone and make the difference with the iPad big enough, so that people never get the feeling that their screen is large enough not to buy a tablet. Does that sound logical?