The OS. That's Apple's strength.
Android is flaky at best, and you never know if anything is actually going to run on it as there's so many damn versions out there now (admittedly iOS is headed in the same direction, but nowhere near as fragmented). All Android screens that I've ever tried, S3 included, have the most irritating lag on the touchscreen that the Apple devices simply don't have. The phone is massive and the screen simply too big for most people, and I find it a shame that Apple have felt the need to pander to the many by increasing the size of the iPhone screen: It's unnecessary. The 4S camera is miles better than the 4 and more than a match for anything out there maybe 920 excluded, and if you can find somewhere in the world that doesn't have an Apple 30-pin plug nearby then I'd suggest you've got bigger issues.
I've not needed a replacement battery for any phone ever, so why would I want to carry around a spare one? I don't need a billion songs on my phone so 32GB is enough for me, but if it wasn't I'd buy the 64GB version. You're making it sound like the choice isn't there, when it is. It's just designed as a one item device, rather than something you carry around a load of different bits for. I haven't been sucked in by anything, I know the weakness of the iPhone for some people. I also understand the goal behind it, that doesn't mean I can't appreciate or disparage other devices as I see fit.
If an Android phone had the screen of the iPhone, I'd seriously consider one. Until such a day comes, I can't see why I'd want to swap the most important feature of a smartphone, the actual interface, for being able to say I can put an SD card in or swap a battery over. Each to their own.