Mark D. Mill:

First, transit. Getting transit directions in China was far more important for Apple than getting US transit directions. Consider just a few numbers:

• The US has ten cities with a population over 1 million. China has 171.
• The US has 34 cities with a population over 500,000. China has 450.
• In 2014, China had 62M vehicles of all kinds registered, in a country of 1.3 billion. This is expected to reach 200M by 2020.

Most people in China get transportation by public transit. Having a mapping service in China without transit directions would be like having one in the US without driving directions. Apple hit this hard:

• Apple developed transit directions for just 10 cities in the non-China world, but over 300 cities in China.
• The non-China cities for which Apple has transit directions have a combined population of about 38M. Just the 9 listed cities in China have a combined population of over 130M.

Second, improved battery life & reduced OS upgrade size. These upgrades do not exclusively benefit China, but they were important upgrades in China. In the last years, as I’ve talked with non-Apple users in China, the number one reason they bought another brand was because of screen size, which Apple solved with iPhone 6/6+. The number two reason was poor battery life. Apple getting an extra hour of battery life was important; getting 3 more hours in battery savings mode is huge for the hundreds of millions of people who commute on public transportation without a power source.

Reducing the size of the OS upgrade, likewise, is important for China and the developing world, where the phone is often the only computer. When I didn’t have enough free space to upgrade, I could just upgrade via iTunes on my Mac. For many iPhone users in China for whom iPhone is their only computer, that was never an option. There are a lot of people still on iOS 7 in China as a result

Every once in a while, Apple puts out "Snow Leopard" type releases that are primarily filled with "boring" refinements. On the surface, people can look at that as a sign that Apple no longer innovates. But really, Apple uses these "boring" OS releases to add important updates that are actually huge to other specific markets.

In the past, Apple focused on features targeted at the enterprise market.

This time, with iOS 9, Apple is going all in on China.

9to5mac:

In order to avoid the sluggishness and bugginess that was most notably seen in iOS 7 for the iPhone 4, Apple has restructured its software engineering process to better support older hardware.

Instead of developing a feature-complete version of iOS 9 for older hardware and then removing a handful of features that do not perform well during testing, Apple is now building a core version of iOS 9 that runs efficiently on older A5 devices, then enabling each properly performing feature one-by-one. Thanks to this new approach, an entire generation (or two) of iPhones, iPads, and iPod touches will be iOS 9-compatible rather than reaching the end of the iOS line.

Great news. In addition to better performance on older devices:

• slow iPhone/iPad upgraders will be able to run the latest versions of third-party apps
• older iPhone/iPad users will get the latest security updates
• app developers can spend less time/resources on supporting older iOS versions
• third-party apps will progress faster