I follow a similar pattern. I went from an S to the S3.
This was in part due to cost. If I am going to spend $600 on a phone, I treat it like any other computer purchase and I expect to get a minimum of 3 years out of the device.
Now that there are phones available that are of almost the same quality, at a much lower price I'll probably make a move - but not for at least a year. While I waited to repair this one I was using a Moto G and I loved it. The screen isn't as big, and it was a relief to get back to my Galaxy in that regard. But I'd say otherwise the Moto G was just as good but it cost less than $200.
People talk about the race to the bottom - and there are some awful Android devices out there but there are also some really nice devices that don't cost such a huge premium and I like to think of them as being part of the race to the middle. The point where I get maximum value.