http://www.dpreview.com/news/2011/12/02/sigmanonOS1750F2p8
Well, maybe because the in-body SR of Pentax is so good! So why OS lenses? ;->
Related:-
When OIS Lenses are Put onto Sensor-shift IS Bodies..
In-Body Anti-Shake Patents Fully Dissected
Sensor-Shifted IS Heats Up the Sensor Much More Than the Video Mode Itself! :-o
When Our Video DSLRs Have High Fever.. :-o ;->