“To some, this repetition is now boring. But I think Apple looks at it the opposite way: they’re perfecting their trick.”
Refining and perfecting have always been some of Apple’s best methods. Consumers often expect a revolution with every new computing device – Apple takes the appliance approach. This is a device you’ll want to use for the long run, and it shouldn’t change radically until it’s time for change.
As for why each subtle refinement costs $500 is a subject of another blog post. Design wisdom, something the rest of the consumer technology industry sorely lacks, is what Apple has in spades.