Well, you already have water running through a waterblock, so what would be the point of adding another medium that is essentially acting in the same fashion-- allowing a liquid to flow through a tube for cooling. Water will do it better than whatever they put in those things.
Also, water cooling is reaching a plateau as far as performance goes. I like to call that plateau "room temperature". If my dad would only let me turn the AC down to 10C I could break the room temp barrier and usher in a new era of simple water cooling
