All the world is not the US, in most places the incentives aren't set up for upgrading phones "just because". But even ignoring that, the benefits to the platfo

All the world is not the US, in most places the incentives aren't set up for upgrading phones "just because". But even ignoring that, the benefits to the platform as a whole for getting to upgrade as many users as possible to latest version should be obvious. And if the top range of 2 years ago isn't good enough for an upgrade, chances are that a lot of the midrange of today isn't either. (That said, if there really is a performance bottleneck preventing the port, the most likely candidate would be the GPU. And once you've made the decision to finally embrace the GPU, there's not anything you can do to fix the problem of going with a lame GPU when speccing out the hardware 3 years ago).