I've wondered this for a while, and know next to nothing about software development, so please excuse my ignorance.
One team takes iOS 8.1.2 and modifies the code, adding the WatchKit APIs and other features, producing a Beta of iOS 8.2.
Another team takes iOS 8.1.2 and modifies the code, tweaking it to fix a ton of bugs, producing iOS 8.1.3.
Don't Apple now have to modify iOS 8.2 to ensure it includes the same bug fixes as 8.1.3?
One team takes iOS 8.1.2 and modifies the code, adding the WatchKit APIs and other features, producing a Beta of iOS 8.2.
Another team takes iOS 8.1.2 and modifies the code, tweaking it to fix a ton of bugs, producing iOS 8.1.3.
Don't Apple now have to modify iOS 8.2 to ensure it includes the same bug fixes as 8.1.3?