Mass-email senders probably would put a unique identifier in the image url (different for all users), so Google will open each image, because it can't know before loading them that it's the same image.
That would essentially render open statistics meaningless and would let Google cripple another industry after the promotions tab and 'not provided.'
I really hope they don't because it's such valuable information when creating email copy...
first one = Google
second one = user