Yeah, had three now two. The two have no issues. What are you referring to?
.
----------
Tech doesn't get as dated now as it used to. For example, I have the same desktop I built in 2008. It's still able to run a heavy mix of cpu intensive applications like video editing, large database jobs and the like. I'm thinking next year I'll update it, maybe.
The 5S, should be good to go for at least 4 years.
Re the iPhone 4, the massive and unmissable lag which occurred the moment iOS7 was installed.
Not so sure about the 5S having a 4 year shelflife, but certainly a couple of happy years followed by a further 12 months of frustration if you're still onboard. These things are engineered to become obsolete. Why make the 5S chug merrily away for years, why would Apple not want you to upgrade? They will make sure that you want the speed 'improvements' offered by the latest tech. These software updates don't generally give much in the way of earth shattering new features, but do slow older devices down.