At least part of it is that folks like my mom just never attach their phones to their computers and ignore any upgrade notifications on their devices, so they b

At least part of it is that folks like my mom just never attach their phones to their computers and ignore any upgrade notifications on their devices, so they basically never upgrade until their son comes to visit. This applies to me as well -- I have two iPads and frankly it's not really worth the bother. I'll probably upgrade them eventually; there's just no hurry. Compounding the problem -- since getting the iPhone 6, I've noticed something I've almost never noticed before on an iPhone: lag. There are times where it seems there's a huge (like 1 second) delay between touching the screen and a reaction. This is noticeable when scrolling in safari. For that reason alone I would recommend against upgrading until the problem is resolved.