As it stands right now, iOS 8 has seen an adoption rate of 83%, which falls short of what iOS 7 did.
While 83% may sound like a huge number, the adoption rate for iOS 8 still falls behind how quickly iOS 7 was adopted by users. In comparison, the latest Android OS, Lollipop, sits at a 12% adoption rate, though their ecosystem is vastly different. With iOS 8, users saw tons of new features, technologies, and experiences.
Users are not only interested in getting the latest and greatest features, but also security fixes and more. Apple has just announced iOS 9, which builds on top of iOS 8, and makes things even better.