I'm surprised nobody is pointing out similarity to Intel's very successful Tick-Tock release cycle - release a new architecture on tick and refine the process on tock

The benefits for Apple are manifold, but the two most obvious are:

1. Keep expectations sane - they can't release a radical new industrial design of superbly high quality every year.

2. Give customers on a 2 year contract predictable value rather than leaving them always waiting for the next awesome device