According to Apple's store Usage Numbers, 85% of users are on IOS 7 and just 12% of them are on IOS 6

With the new design and features in the IOS 7, I'm not surprised when I see the adoption numbers of Apple's IOS.
And as any time, apple has updated its adoption numbers of the IOS 7 which hits 85% of IOS users while just 12% of these users stay on IOS 6 and 3% on earlier versions of IOS like 4.3 and 4.4, but even with these numbers we can say that it will stop there, because the most of apple users who didn't update to IOS 7 has one of these reasons:

1. They don't like the new design and the features of IOS 7 so they decides to continue using the same style
2. They have locked devices and they're using UltraSn0w to unlock their phones
3. They have old devices like iPhone 2G, 3G, 3GS ...

Apple didn't precise which version of IOS 7 has the most number of adoption. As you know the company has released the official version of IOS 7.1 which come with many security fixes and improvements, but the problem here is that the IOS 7.1 patch the jailbreak exploits so this will stop many users from updating to this version until the jailbreak is released.
That's why I think that the most of IOS 7 users are on versions that work with the Jailbreak. 

Source: The Next Web