The good news is that the oldest versions of Android are almost unused. Combined, Android 1.6 Donut, 2.1 Eclair, and 2.2 Froyo total just 4.6% of devices accessing the Google Play Store. These versions of Android shipped on brand new devices in 2009 and 2010. Android 3.0 Honeycomb is practically extinct. It is installed on only 0.1% of Android devices. Honeycomb was specific to tablets.
Android 2.3 Gingerbread is holding on for dear life. It has long been the most widely adopted single version of Android and was, at one point, installed on two-thirds of all Android devices. It has lost ground to newer versions of Android, but very slowly. As of July 8, Gingerbread was on 34.1% of Android phones. That's far too many, given how outdated Gingerbread now is.
[ Google wants to be on all platforms. Read Google Tweaks Android, iOS Apps. ]
Android 4.0 Ice Cream Sandwich is on nearly a quarter of devices at 23.3%. Android 4.0 first debuted in 2011. It was supplanted by Android 4.1 Jelly Bean about six months later in May 2012. Android 4.1 Jelly Bean is installed on 32.3% of Android devices, and Android 4.2 Jelly Bean, which arrived in October 2012, is on 5.6% of devices. Together, the Jelly Bean versions (4.1 and 4.2) total more than Gingerbread with 37.9%. Anything running Android 4.0 and up is considered the modern version of Android.
The newer versions can thank their growth in part to the large increase in Jelly Bean device sales. Most new devices shipping today, including flagship smartphones such as the Samsung Galaxy S4 and HTC One, run Jelly Bean out of the box.
Still, only a handful of devices have access to Android 4.2 Jelly Bean, which is why it remains at just 5.6%. The Nexus line of hardware, including the Nexus 4, Nexus 7 and Nexus 10, are all running Android 4.2.2. The only other devices that have access to this version are HTC One and Galaxy S4 variants being sold directly by Google with stock Android installed. These devices just became available from the Google Play Store recently, however.
By way of comparison, Apple recently offered a look at iOS fragmentation, such as it is. According to Apple, just over 90% of all iOS devices are using iOS 6, which was released in September 2012. iOS 5 makes up for most of the remaining 10%, with only a small percentage of devices still running iOS 4.
Apple is still better at delivering core updates to its smartphone platform than Google.