I just had detailed conversation with a Nikon rep at NAB show about this. It started because I pointed out that even though some spots on the grip are protected the grip itself is not even moisture resistant. For example moisture can get through under the tightening wheel very easily. He agreed with me and we started talking about the cameras. Basically on these types of cameras there are seals, many of them but camera itself is not even moisture resistant. It only takes one entrance point and that is all she wrote.
But I had my cameras in the light rain and never a problem. So it all depends on the luck I guess.