Android developers just published the information about the relative number of devices that share a certain characteristic, such as Android version or screen size.
According to Official source, Jelly Bean version 4.1 and 4.2 acquired 28.4% of Android device share, about 3.4% increment compared to the last month data where Gingerbread Android 2.3 is still in leading position which exists in 38.5% devices but it lost around 1.4% share in current month.
Ice Cream Sandwich Android 4.0 has secured 3rd position with a device share up to 27.5%, around 1.8% lose compared to last month report where Ice Cream Sandwich was able to capture 29.3% of total Android device.
“Each snapshot of data represents all the devices that visited the Google Play Store in the prior 14 days and Data collected during a 14-day period ending on May 1, 2013”.
It's just a monthly report and yearly report may change and the next version known as Key Lime Pie is going to be released soon.
Source: Android Developers