One of the main issues with Google's Android operating system is the lack of after-purchase support. Manufacturers aren't required to keep devices up-to-date with the latest versions of Android. This means app developers have to write code that works on various different versions of the operating system, making it harder or impossible to do certain things on older devices.
That's why it's both good news and bad news that Jelly Bean's adoption rate has hit 33 percent. It's good that more users are adopting the latest Android version, but it's also bad because only 33 percent of users have the latest version. 25 percent are still on Ice Cream Sandwich and a whopping 36 percent are still on Gingerbread.
It's important to note that Google changed the way it calculates usage percentage:
Note: Beginning in April, 2013, these charts are now built using data collected from each device when the user visits the Google Play Store. Previously, the data was collected when the device simply checked-in to Google servers. We believe the new data more accurately reflects those users who are most engaged in the Android and Google Play ecosystem.