A phase change setup is needed for freon because that is the way it cools. That is what the compressor is for. Freon is initially compressed into liquid form and transported to a heat source, in the case of computers your CPU. When it is heated it evaporates into a gas and when this happens it carries a lot of heat with it. Ever notice when you place rubbing alcohol on your skin and blow on it your skin feels cooler. That is because as the alcohol evaporates it takes away heat from your skin.
Now this won't work in a conventional WCing setup because the tubing would have to withstand the changes in pressure. Half of your cycle would be gas the other half liquid. Also in liquid form the freon is very cold and condensation prevention techniques would have to be done on the tubing. These are some of complications that arise from such a setup. To simplifiy things, take a look at the parts of a VapoChill case or a Prommie and compare it to your WCing system. Everything the VapoChill or Prommie has will have to be done to your WCing system for freon to work effectively.
Now the freon in gas form is brought into a radiator/condenser combo where it is cooled and changed back into liquid. The liquid is then recirculated back to you CPU. Prommies and VapoChills work under the same premise.