What you will need to plan for however
is diversity in platform versions.
Because Android OS is itself just another
component, manufacturers are free to
use whichever version best suits a
device’s overall capabilities and
(And if a manufacturer has highly customized their
build, they may not be able to immediately update
it each time Google releases a new version).
Jelly Bean (2012)
Ice Cream Sandwich
Older versions 2.5%
Source: developer.android.com, September 4 2013