Apple's target customer is a person who doesn't know/cares about how tech stuff works, even more when we talk about an iOs device. It doesn't have public specs, it doesn't even have a file manager for God's sake. If that person has an iPhone 4s, and Apple says him to update, because the phone tells him so, he does it, because it's Apple and "it just works". For a lot of people the difference between an iPhone 4s and an iPhone 6 are aesthetics, screen size, touch Id and price, just that, they even have the same OS. The reality is that iOs9 has quite some lag on an iPhone 6. I suppose that on a iPhone 5s it is quite bad and 5-4s it is just crap. There is no excuse for this, the only reason being pushing that people to upgrade their devices obviously, which is very legitimate since it's a company with shareholders and so on. But this is a forum, full of naive users as usual, those people who think Apple used 1gb of ram because power efficiency or silly things like that, not for increasing their profit margins.