Gruber hit on something in his iPhone 4 review that made me stop and think before I could get past it:

Apple seems very confident about the precise size and dimensions of the iPhone display: 3.5 inches, with a 3:2 aspect ratio. Not 3 inches. Not 4 inches. In fact, Apple seems very confident regarding everything it decided for the original 2007 iPhone. There are no new buttons, or even moved buttons. The Retina Display is emblematic of the iPhone 4 as a whole, both hardware and software: the same fundamental idea as the original iPhone, but clarified. It hasn’t really changed so much as improved — like the same picture in increasingly sharper focus.

[…]

The iPhone 4 feels like a major step toward an idealized iPhone form factor.

He’s right — the iPhone 4 is an obvious, healthy evolutionary descendant from the original iPhone.

Apple finesses and evolves its designs over time.

The first example that came to mind was the iMac.

When the iMac G3 was announced, its simple, all-in-one design* was highlighted heavily in Apple’s advertising. In the three years it was on the market the core design remained intact. Every iMac G3 looked basically the same, even though the external treatment ( Flower Power, anyone?) and internal components evolved quite a bit.

In 2004 the original iMac G5 came out and the design was praised for its simplicity. Apple highlighted the design in a product video, promoting the design — tying it to the iconic look of the iPad.

Apple has moved to aluminum and glass, but the iMac of today is much like the iMac of six years ago, just refined.

Another example that comes to mind is the pre-unibody MacBook Pro. While the case looked very, very similar to it’s PPC-powered ancestor — the PowerBook G4 — the MacBook Pro packed all new internals, which, at first, were not laid out very well. But over time, Apple’s engineers made the machines more easy to work on, and by the time the machines were phased out, even the most complicated repairs were simple to carry out.

Likewise, the insides of the pre-unibody MacBooks also evolved over the years, losing weight and gaining rigidity and simplicity.

This philosophy pretty genius, actually. Apple likes to announce one new product at a time. (At most they highlight a single line, like the yearly iPod update in the fall.) By revamping the same design over and over, it makes any major redesign a big deal. Throw in some Stevenote time and — boom — instant news story.

Another upside of this mentality is that it lets users upgrade their gear with ease of mind that they will be able to use it. Anyone who can use Snow Leopard can use OS X 10.2 pretty easily. Anyone who has an iPod can use the original iPod without skipping a beat. iOS 4 operates basically the same was as the original iPhone OS did.

It’s tempting to think of this philosophy as being a lazy one to have. In fact, it’s the opposite. A refinement is basically a critique of past products, and finding ways to improve existing work takes a great deal of honesty and attention to detail.

Of course, Apple creates artificial refinement opportunity. Why doesn’t the iPod touch or iPad have a camera? Why didn’t the 13-inch aluminum MacBook have a Firewire port?

Upgrades, baby. Upgrades.

—– \* Of course, the iMac harkens back to the original Macintosh in many ways, including this.