for android i think the battery discussion and sd card storage are more relevant than on the iphone. why?
the iphone typically has good battery life given comparable usage and battery size to an android phone (non-rooted). android phones can run through battery faster due to multitasking functionality, lte, etc. it's easy to lose track of how fast your battery is depleting or how long you can go before you need to recharge. being able to swap in a fresh battery is a huge benefit to power users or a huge relief to users that don't monitor their battery closely. also consider the flexibility of being able to put in an extended battery for even longer up time.
the sd card storage provides a "safe zone" for media on an android phone. updates, upgrades, flashing roms (for rooted phones), can put on board storage in jeopardy of being lost. i've seen a lot of cases where galaxy nexus users lost all of their data while performing a simple carrier upgrade. an sd card can be easily removed which pretty much eliminates the possibility of data being lost by accident. it also makes data storage and arrangement a cinch since you can just pop out the card, plug it into your computer and have it recognized as a drive. sometimes computers\android act funky when you plug in your phone and how it recognizes internal storage. for iphones i suppose they have some of the same risks, but not as much since most of the onboard storage is saved in itunes.
so...in terms of the sg4 and the one, user preference is a significant driver, but the practicality and flexibility of sd card storage / swappable battery is an undeniable advantage imo.