THIRD PARTY SUPPORT
The original iPhone, even before the AppStore, STILL had more peripherals, cases, and forum support than any other model of phone since (perhaps combined).
Then the AppStore came, jailbreaking was no longer necessary to have the phone on par with the Symbian OS that was the best alternative at the time, and it's been all downhill since.
Now every iDevice I buy I have an INSTANT software library of 1000's of apps I own, they are constantly innovating with new apps/games, and the jailbreak scene has taken customization to the same level (if not beyond when you consider polish and usability) of the Android phones that people always gripe have more "customizability" as the main buying factor.
If you want the best of every world, it is impossible to beat a jailbroken 5S. My buddies at work (including a guy who was like me pre-iPhone and buys a new phone quarterly) always show off their new non-iPhone, only to get something new a few months later.
People who own iPhones buy NEW iPhones. At a much greater %. I don't have the statistics to cite, but I believe it's almost double (and it would be more, were it not for an admirable showing from the SGS line). If you don't like the phone enough to buy it's successor when the hype dies down, then that's enough evidence to me that I'm not missing out
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There are more subtle reasons too: like first party support. Have a problem? Go to the Apple store. Chances are, especially if it's a defect, you're leaving THAT DAY with the problem solved. There is NO other phone out there with the support network Apple has.
I could go on and on and on, but it's an easy choice. It is, has been, and will likely continue to be for some time. Period.