I think Kishi put this in here to demonstrate that they can't be killed, to show the readers of the manga and watchers of the anime that edos are diifficult to tangle with.
Is it possible orochimaru allowed them to be blown up? To show hiruzen what happens when they are fatallly wounded. This is just thinking out loud of course, can't prove it.
Of course somewhere i remember that edos have their same abilities, however i clearly remember Gaara's father saying something like "I wanted to kill you a few seconds ago, but my body wouldn't let me" Sorry, not exactly a direct quote, it was when he was standing around with all the other old kages in the desert. It seems Edos can be restrained when it needs be. This is my only answer to why both tobirama and hashirama got paper bombed. ...Also more important for the reader to understand what edos abilities are too.
. Oh my, you finally read my username.....Well done. 
