As far as I know there is no difference, we use the same charger for iphone, ipad, ipod, etc.. and no problem.
There is a statement from Apple that confirms this : http://support.apple.com/kb/HT4327
Message was edited by: Tatawaka
Wrong statement! haha
Here is a thread regarding this: https://discussions.apple.com/thread/2397877
In summary, it'll work, but charging will take more time.
Message was edited again by: Tatawaka