I posted this elsewhere, but it bears repeating:
Apple phones are designed to do what they do smoothly and consistently, and they do that better than anyone. Also, the updates on iPhones are consistent, and not held back by carriers and fragmentation. What will the S4 be running in 2 years, when the 5S is updating to iOS 9 just 10 days after announcement? Possibly KitKat?
Now I love Androids just as much as anyone, but I will admit that Apple has their stuff together when it comes to satisfying their customers, whether it be timely updates every year or customer support ( which no other phone manufacturer comes close).
Why do you think that they are #1 in customer satisfaction polls year after year?