It seems that armature relation is lost between duplcate mesh with armature modifier and duplicate armature.
I tried your blend in 2.70. This relation seems to work better but in 2.70 because deformed item is supported.
But there is also another big problem in 2.70, constraints between rigidbodies duplicates are ignored, too.
So, if you look at .blend in 2.70, there is a deformation but it is a very ugly one.
In 2.71, there is no deformation at all. I am not sure it is worst.
I don't know what are approved limitations of dupligoup use in BGE.