Lots of threads on macrumors and other sites that highlight what your asking.
I upgraded my one year old 4S and it is huge difference to me. People just don't like to change something they like right now and 4S is good phone overall. iphone5 is totally different beast. It jumps on speed on anything you are touching with fingers, it is amazing on size and weight, it is better on screen resolution, it is blazing fast on LTE etc. If you don't thing anything above is important than get or stay with 4S.Some people say the Iphone 5 isn't a big upgrade from the 4S. So here's a question what's missing from the Iphone 5 to make it a massive upgrade?
iPhone 4/s = Mercedes.. iPhone 5 = BMW. More athletic and less refined.
okay, that was probably a bad example depending how you look at it.Bad example, MB having much better meaning in auto sports than Bmw, presently no Bmw at F1 racing as example and plenty of MB there. MB having many sports models, not cheap but not less then BMW in power and speed.