Well that is certainly an exception, but I'm thinking more of the diy type builds, and fan powered. I probably should have mentioned that.
The voodoo stuff is pretty expensive. I've actually never done water cooled, I've actually tried to avoid it for other reasons, but you also have to take into account the noise of the motor.
From what I've read, many of the motors in DIY watercooling don't necessarily strive for silence, but rather power, so they end up being not much quieter than air cooled alternatives.