If I remember correctly cables were coded as tile entities, which pistons do not like to move. It's in the Mojang code. Not IC2's faullt.
As far as I know mods are meant to change the existant code. I am not talking about anyone's fault, I simply saw a feature that could be in IC2 that isn't right now. Maybe it doesn't serve of any purpose to enable pistons moving IC2 blocks, but I think someone would find interesting for some bizarre machine.