I never heard of a company closed liquid cooling setup leak and spoil stuff since the liquid used is mostly very low conductive mixtures. But still haven't heard of a closed liquid loop leaking unless messed up by the buyer real bad.
Maybe do a quick Google, then. While it's a minority of users that are affected, closed-loop water coolers like those provided by Corsair have leaked. Can you tell me where it says they use low conductive mixtures, too? First I've heard of it myself.
Another reason for choosing a water-cooler is that not all PC users like the idea of hanging a heavy weight off of their motherboard. Some after-market coolers weigh up to (and sometimes in excess of) 1kg.