>>  you can simply check your balance anytime

I guess my point is that coins are virtual, they are just numbers.   

and so if somebody steals your coins, you might still have them also.   there could be multiple copies of the same wallet.   they haven't vanished from your harddrive.   just a copy-and-paste operation .

And so, is the wallet smart enough to realize this?   is the online exchange smart enough to realize this?      in real time - not 3 months later when you attempt to spend the coins, and find out they are invalid now.