This is normal, and for good reason. The 960/970/980m are some power hungry and heat inducing chips. If they were not clocked down when on battery two things would happen.
The first is the battery would drain very quickly, and while you might says that's ok, it actually drains so fast it can harm the life of the battery.
The second is these chip run very hot, if you take the heat from these chips and combine them with the heat of a rapidly discharging battery it can become to much in the confined space. While ASUS RoG laptop have best in industry cooling, It is still a lot of heat.