Most of iOS 7’s redesign was probably decided on “valid” factors: the iOS UI was looking pretty dated and had accumulated a lot of cruft, and Apple clearly loves and believes in the polarizing new design. But it also comes with a number of convenient defensive advantages.

Since iOS’ launch in 2007, people have devoted a lot of time and money to copying the UI. Samsung, of course, is the biggest offender, but the copying has gone far beyond them: almost all modern smartphones and tablets have parts that resemble the old iOS UI. (Some have more parts than others.) iOS mimicry has even widely infected web design, especially those horrible “mobile” blog themes that try to look like an iOS app.

The entire tech industry has been homogenizing and commoditizing iOS’ appearance so much that after six years, iOS no longer felt exclusive, unique, or premium to most people: it felt like the norm. Apple needed to shake things up to keep their premium edge, and they went all-out.

Since WWDC, every iOS-imitating UI looks ancient. Soon, they’ll start to feel obsolete. Most imitating efforts will need to be redone or abandoned to look current. And what will happen if people try to imitate iOS 7?

Presumably, Apple has a few new patents for iOS 7’s interface and behavior. As we’ve seen, this won’t prevent copying, but it can at least increase the cost. Any efforts to copy the new UI are going to have a dark cloud of potential litigation hanging over them.

Copying iOS 7 is going to be a big problem for cheap hardware. iOS 7’s appearance and dynamics require a powerful GPU and advanced, finely tuned, fully hardware-accelerated graphics and animation APIs. This will hurt web imitators most, but it’s also going to be problematic for Android: while high-end Android phones have mostly caught up in GPU performance, and recent Android versions have improved UI acceleration, most Android devices sold are neither high-end nor up-to-date. The gap is much wider in tablets, and even “high-end” tablets usually have insufficient GPU power to drive their high-DPI screens.

Apple’s even attacking Android’s screen technologies by making heavy use of 1-pixel-wide lines on Retina screens. Most Android phones have high-DPI screens, too, but their feature-checklist battles have actually driven many of them to have too-dense resolutions for 1-pixel lines to be useful. And many Android phones, notably including almost all Samsung Galaxy models, cheat on resolution by using PenTile screens, which poorly render text and thin lines.

The theme is clear: iOS 7’s UI requires some of Apple’s biggest strengths, and efforts to copy it will be hindered by some of Android’s biggest weaknesses.

iOS 7 is also going to be a problem for cross-platform frameworks. Fewer assumptions can be made about the UI widgets and behaviors common to all major platforms. And any UI targeting the least common denominator will now look even more cheap and dated on iOS 7, since the new standard on the OS is so far from the old one.

But there’s also a huge win in developer attention.

In early January 2010, Google’s developer relations group sent me a Nexus One to experiment with, unprompted and with no strings attached. (This was very nice and generous of them.) Seeing a future where Android mattered, I started experimenting with different text settings for Instapaper’s web reading view to look good on its PenTile screen. On January 25, I published some of my progress.

Two days later, the iPad was announced. I never had time to think about Android development again.

Apple’s competitive message to developers during the keynote was clear: iOS is doing great, it’s the best platform to build apps for, and you don’t need to think about other platforms. iOS 7 reinforces this even further: whatever app developers were planning to do this fall is probably on hold now, because everyone’s going to be extremely busy updating and redesigning their apps for iOS 7. Anyone thinking about expanding into another platform now has a more pressing need to maintain marketshare on iOS.1

It’s a power move — one that I think Apple still has the power to pull, but just barely. We’ll see how it works out in practice.