Well, watercooling is even more funny than these large air-coolers :)
You have one "heatsink" that's REALLY large (radiator), and 2-3 big fans on it (if you want it to cool whole system), so you're already at the same weight/size/fans amount us with common air coolers are, plus you have to bother with liquids and pumps :p: ;)
Now, if you would have fridge-cooling, that would be altogether different stuff :D