There’s no doubt that a lot of Apple users have upgraded their smartphones and tablets to iOS 7 so far but there may be a sizable portion of the company’s user base holding out. MillennialMedia has noticed that adoption of iOS 7 seems to have lagged behind where adoption for iOS 6 was one week after its release. Specifically, MillennialMedia has found that “while the 185% daily growth for iOS 7 was impressive, we looked back at the first week of growth for iOS 6 and saw that it grew an average of 264% daily.” The firm speculates that the major changes that Apple made with iOS 7 may have spooked some users who would have otherwise rushed to upgrade their devices, although it admits it has no firm data to back this up.