Google Hangouts was probably the first Android app update that was gradually rolled out. Then Google officially added support for
staged rollouts and any Android developer could use it.
"If you like, you can release your app via a staged rollout, starting with a small percentage of your userbase and then increasing it. You can set and modify the percentage for the staged rollout on the APK section of your Google Play Developer Console, on the Production tab, while keeping an eye on crash reports and user reviews, to make sure users like new functionality in your app. While a staged rollout is in progress, you won't be able to update your production configuration. You must publish the staged rollout to 100% of users first."
You've probably noticed that Google used it for the latest Maps and Chrome updates. Google announces the updates, but you can't install them because they're gradually rolled out. Even if you go to the app's Google Play page, you can't manually update the app. You need to find the APK files and install them from various sites, while hoping that they're legit.
While staged rollouts are useful for developers, they're annoying for the people who want to try the latest features. Google uses a similar approach for web apps like Gmail or Google Docs and for Chrome updates, but there's a trick to
manually install the latest Chrome update: go to the about page.
Here's a similar idea for Google Play: limit staged rollouts to automatic updates and allow users who want to get the latest updates to do that by visiting Google Play's app pages and manually installing the updates.
