i always love to drive my nano then my getz (CNG). RWD are more responsive and we can feel the power of engine in it. FWD is good in turning then RWD .
we can call NANO a RWD but since its engine is located in rear itself, its cheap and easier to have it RWD. also, it powers 38 HP, which is not enough if they made it front engine - front drive (like M800 which feels under power on highways with AC, while nano never feels underpower on any road with AC ) thats the main advantage of RWD.