It would be silly to sit here and pretend that fragmentation doesn't exist in the Android ecosystem, or that Android 4.0.x (Ice Cream Sandwich) and 4.1.x (Jelly Bean) are going to reverse unify Android devices. Be that as it may, the latest Android builds are making headway, particularly Ice Cream Sandwich, which is now installed on 15.9 percent of all active Android devices.
Jelly Bean adds another 0.8 percent to the pool of devices running an Android 4.x build, and though that's a rather meager number, also keep in mind that it practically just came out and is only available (officially) on the Nexus 7 tablet. Put into perspective, that's not bad.
Android 2.3.x (Gingerbread) still claims the lion's share of Android devices with a 60.6 percent share of active Google devices, followed by Android 2.2 (Froyo) at 15.5 percent, Android 2.1 (Eclair) at 4.2 percent, and Android 1.x (Cupcake and Donut) accounting for a combined 0.7 percent, which is less than Jelly Bean.