This is all spin from Maddow. They don't think they've won it, but they want to present an illusion of inevitability. Why? Multiple reasons. One, it helps with fund raising. Two, it helps to mobilize the base and quell the unease within the party that was very apparent at the convention. Three, they know she can't campaign hard because of physical limitation and a general lack of stamina, and this is their cover story. Four, They're hoping to suppress the enthusiasm for Trump.
If they thought she had it in the bag she certainly wouldn't have been out there giving that horrible speech yesterday, and wouldn't have been opening a jar of pickles on TV.