The problem is, I don't do that much with my iPhone. I commute by bike, so the large screen is usually wasted - as is the gigantic GPU power of the 6S.
I don't watch movies on it, either.
WeatherPro, various news-apps, my mobile-banking app (which still works great on my 4S), a shopping-list, reminders, calendar, some email, messages, a bit browsing during lunch, some public transport timetables / travel-related apps, the meetup app, camera, photos, maps.
I've bought two games, shortly after I got the 3GS. I don't play games.
The camera is the thing that in the end will get me to buy one. And maybe the M9 chip.
The reason there is no "small" phone anymore is probably also pricing.
It would have to be priced identically to the larger phones - or people would just buy the smaller one.
And then, developers would have a problem writing software that uses the latest features...
So, price has got to be almost the same - and then people become aware of the fact that the pricing of Apple products isn't that much related to the cost of components...
So, it's a Pandora's box that you don't want to open.
But come next year, the 5S will fall out of the lineup. It will be interesting to know what happens then.
There could be a place for a "shrunken" iPhone 6.