If you press your hand to the bottom of a heat sink and warm it up, then turn the water pump on, it feels like water just washed over your hand, the metal cools down as soon as the water passes over it.
Some people seem to think air can be better because at idle, heat pipes can end up a few degrees cooler. Ultimately what you want though is heat dissapation, ideally without super powerful fans and water cooling is far better.
If you move the heat away from a small area quickly, you can easily spread the heat out into a MUCH bigger radiator which will cool more efficiently with air. A nice water cooling loop effectively increases the radiating surface area, with a nice side effect that it moves the heat further away from the rest of the computer.
It doesn't ignore that at all, the whole point is to move the heat from the tiny CPU to a big radiator with a lot of surface area. Air is a terrible conductor of heat compared to water, which pales in comparison to metal, but even metal doesn't move heat as well as flowing water.
Some people seem to think air can be better because at idle, heat pipes can end up a few degrees cooler. Ultimately what you want though is heat dissapation, ideally without super powerful fans and water cooling is far better.