I know this answer is really late, sorry, but no, the current that you have in your house is Alternating Current (AC) which means it's flowing one way, then it stops, then it starts going the other way, so both pins do the same thing, the job of your charger is to transform this into direct current (DC which flows one way only and is required for both your iPad and battery operation), the charger is also a transformer which reduces the voltage from approximately 120 volts to 5 volts (when using iPad charger) or to approximately 3 volts (for iPhones), this process releases a lot of heat.
So heating is completely normal, the problem is that when the transformer (white "box" of your charger) heats too much it may end up becoming useless or, in the most extreme cases, catch fire. So keep your charger in a ventilated or cool place and use a wall socket instead.