The killer feature is that it is designed by Apple in California.
I don't normally post in these debates, but you (for me anyway) just summed it up in one!
I consider Apple's products to be premium products. Yes there are cheaper alternatives, but I personally don't like the fragmentation that Android brings for example.
I a fan of Apple's "walled garden to an extent, in that I feel the reason the product (in this case, the iPhone) works so well is that you have a device where the manufacturer designs & implements that hardware
and the software and that's what pulls everything together
IMO.
Also, the fact that if I have an issue with my Apple my device, I like the fact that I can take it into any Apple store and get it sorted/swapped on the spot.
In the UK, with any other make of mobile phone you are on your own in the event of a failure and you will lose the device while it goes off for repair (either sent by the shop you bought it from, or the network operator that supplied it.
Either way, you've lost it and you will be phone-less until it gets returned (often with a "no fault found when tested" note attached, despite being away for "repair" for 10 days or so.
The only way to ensure you have "a" phone while it's being repaired is to take out (pay extra for) one of the myriad of insurance policies that the shops/providers offer you and more often than not, it won't be a like for like you get while your phone is away, it will be "something to tide you over".
For me, these are major driving factors in buying an iPhone over any other device (not just Android).
I actually like iOS and the way that it works. I do J/B it, but only for a couple of tweaks like 5 Icon Dock and SBSettings. I could easily live without these and it would certainly be nice for Apple to implement the features, but when I get an i5 if there's no J/B available I'll happily live without them.
I love my iPad and I love the way stuff just sync seamlessly between devices.
Am I an Apple fanboy? Maybe, but I appreciate value in quality products and that's why I can't see myself moving away from the iPhone.
Not sure if that adds to or takes away from this particular thread/debate, but I thought I'd chip in my $0.02!