In some ways, I think people bought a tablet and the time it takes to buy a new one is much longer than a phone. Plus, a lot of people are not doing well yet or in the first part of recovery.

one theory might be that iPhones are publicly visible since you are using it at work and your friends see it (so you are more likely to keep upgrading to show that you have a taste for luxury), where as iPads can't be carried around in public due to it's large size and remains parked at home.

ex. (warning hypothetical stereotypes here that I just thought of) J.A.P. wouldn't want to be caught dead with an old iPhone (what would Samantha think of her now) but might be using an older iPad if it means she can still play Candy Crush at home before bed and tucked away in a drawer.