As of September 19, Apple reported that, based on visits to the App Store, some 52% of activated devices were using iOS 9. I presume a hefty portion have already upgraded to iOS 9.0.1. This news was sufficient to earn an Apple press announcement, and it’s no wonder. But it also was greeted by skepticism in some quarters. You see, third-party companies that record online metrics, such as Mixpanel Trends, were reporting a far lower figure.
Usually, it’s the reverse. Apple’s numbers tend to be conservative. Now it may well be that the figures were skewed by the fact that more people accessed the App Store on multiple occasions to download updates to be compatible with iOS 9. The number of changed apps, to some, appeared to be far larger than were available after iOS 8 arrived. The App Store gathers these numbers based on the OS a device is running when it contacts the store.
In my case, I counted 28 app upgrades since installing the release version of iOS 9 on September 16th. Some involve the same app that required additional changes. But I also downloaded a bunch during the time I was running iOS 9 betas, so this issue becomes a little more complicated.