iOS 5 already running on 1 in 3 capable devices

Apple revealed Monday that iOS 5 (s aapl) was already being used by 25 million iOS device owners, and now a Localytics study to be released Tuesday finds that 1 in 3 devices capable of running iOS 5 are already doing so, not even a week after its release. Even when you don’t count the iPhone 4S in the figures, 31 percent of eligible devices are still running iOS 5.

The iPad 2 and the iPhone 4 are the strongest in terms of devices using iOS 5 (besides the iPhone 4S, which comes with it pre-installed), which makes sense, since users with the latest and greatest hardware would also want to be on the cutting edge of software. Of iPad 2 owners, 36 percent are already running iOS 5, and of iPhone 4 owners, 35 percent have upgraded.

The original iPad is the next closest at 33 percent, while the 3GS trails a bit farther behind at 27 percent. Coming in last are the iPod touch models, with the oldest one that can accept the update, the 3rd generation touch, beating its more recent iteration by 6 percentage points at 23 percent. By comparison, take a look at Android adoption rates; it isn’t all the fault of users choosing not to update for Google’s (s goog) mobile OS, but Apple’s ability to get users on board with current-version software is a definite strength for its app developers.

Localytics discovered this by analyzing all device usage on its mobile app analytics platform between Oct. 12 and Oct 17. Mobile users tend to update more quickly than desktop users, but that’s an impressive adoption rate even still, especially considering how plagued the initial launch was with server errors and other problems reported by users.