They would not include watercooling as a stock cooler with there cards as that would push the price up and not fit in many PC cases..
On the contrary, most, if not all PC cases have a 120mm/140mm fan at the back. That can usually mount a 120mm rad on the same spot, even if it's not mentioned in the case specs. I mean, the holes are the same.
It would, however make Crossfire very hard for most cases.