I've been using the iPhone since the very first version. Yeah, I dabbled with a couple of Android phones in between, but all in all, I keep going back to iOS based phones.
Right now, I've got an iPhone 5 I purchased on the T-Mobile monthly payment/no interest plan, and still have a fair number of payments to make before it's paid off.
I didn't see the point in taking a further loss to move up to a 5s, even though I do think the fingerprint sensor is handy, and the camera improvements would be "nice to have". Knowing Apple's roadmap for phones though, they generally make it worth your while to upgrade every other release. If you still had a 4s, then the 5s made sense as your upgrade. If you were on an original 4, then the 5 was a smart upgrade when it first came out. Upgrading more quickly than that usually means you're paying a premium just to say you have the latest thing.