The URGE to get a new one is irrational. We dont see that on PC when a new graphic card comes out or something. The iPad replacement pace is massive and hysterical.
Why is it hysterical or irrational? The new model provides significant advantages to the consumer.
It costs about as much as a fancy new video card, and is much easier for users to replace than a video card. Plus, they can sell the old one, or hand it down to spous/kids/etc.
The devices aren't disposable, either. They hold value, and it's easy enough to sell the old one. Nobody is throwing away an iPad.