They are totally the same, you don't need to worry about this..
DefBref said:Although you are correct about no need to worry, they are not totally the same! The ipad charger (as mentioned in post#2) has a higher power output (10w compared to 5w for iphone charger). This means you can't use a iphone charger to charge a ipad as there's not enough juice. The other way round is fine as explained in post #2.