Sorry to beg a minor point, but it's the money. Edwards brings his own sizable fortune all the way in (a candidate can give himself as much money as he wants). Now, the guessing game is whether that would bring the John-John finances up enough so that they can decline the $75 million in public financing and the 6-week hole they'd be in.
The polls were most likely secondary to the hard, cold cash.......although they were factored in.
Both really good reasons to pick a VP candidate, eh?