Battery would be the reason for me to get the S4. Not because I go through multiple batteries a day but because batteries deteriorate over time. An iPhone 4S in my family would last only half a day after just 6 months of relatively heavy use. With removable batteries, there would be no such worries in later time. And when the upgrade time comes, I would get a new back cover for the S4 so that they would look new again (hopefully) and sell them. One thing I liked the iPhone 4/4S design so much compared to the iPhone 5 was how well they aged. Seeing all those damaged iPhone 5s (scratches, dents, nicks, etc,.) at Apple stores was a huge turn-off.
For my parents, I did not need to persuade them or anything. They wanted the S4 themselves at the store because of the screen. That has been a common theme among my friends and co-workers as well. AMOLED screens have a huge advantage v. LCD in indoor display for average consumers from what I've seen. I was not surprised to hear that Moto X is being equipped with AMOLED, either. They simply pop and people go wow.
Myself, I'm upgrade-eligible but sticking to the N4. It may be my loss not to use the upgrade but I just love my N4 that much. ^_^