I just used iOS 7 on an iPhone 4S for the past 4 days while my new 5s was being shipped and I don't see what all the fuss is about. It definitely wasn't as smooth as my old iPhone 5 but I didn't really see any major issues with it.
Contrary to what you assume, I actually make money on my iPhones. I always get a subsidized upgrade when I upgrade my iPhone and then I sell my old one on eBay for twice the price I paid for it in the first place. It's foolish for me NOT to upgrade each year.