Watercooling is basically quieter then aircooling because you have full control of "heatmanagement". With aircooling you have to lose the heat on the place where its created, where sometimes isnt much room or ease of installation. Also with aircooling every device creating heat needs to have a fan mostly, which adds up for most computers with many "devices"
I don't agree with your statement.
When heat is generated you have to transfer it away from the source in some way. The heat can be transfered through solid material (e.g. metal), liquid (e.g. water), gas (e.g. air) or through a material that undergoes phase-change (e.g. heatpipes).
Usually this is used to transfer the heat a small distance and then transfer to another media (often air).
For a typical water cooled system lets have a quick look at Seals picture in this thread. He uses 5 fans, 1 pump and 1 radiator to cool his system.
In my typical air cooled system I use 3 undervolted fans to cool the system.
In a classic water cooled system you can decide where to put your radiator and most users choose to put it in the chassi with one or 2 fans attached to the radiator. This is not fundamentally different from having the same fans in the same location and use ducting to cool components.
I see no major differentce in control of heat management.
If you go to the extreme (like your system seems to be) by using huge heatsinks on the outside of the chassi your main concern will be how to transfer the heat to the heatsink and also make sure most of the heatsinks heat is dumped on the outside of the chassi.
The equivalent of your system without water cooling is Zalmans new chassi. It uses heatpipes to transfer heat to two big heatsinks (the sidepanels) and cools CPU/GPU/NB. It also uses heatpipes to cool HDD, but due to the low heat generation they dump the heat inside the chassi. It also cools the PSU passively, but I believe that heat is dumped out through a third heatsink.
Comparing your system to Zalmans cooling system I find that you have at least a pump going and they have no moving parts.
One fundamental difference is that you "collect" heat from all devices, when the Zalman chassi strives to take heat from the source the shortest way to where is can be cooled. From a scientific standpoint this has to be the best way to cool things, but perhaps not always the most practical solution or the most inexpensive.
The only two drawbacks I can see with Zalmans solution is price and added total weight of computer box.
I believe this is almost the same as drawbacks with your system. I guess you have lower price, and added work (depending on your hobby this is either good or bad), and your system can leak water. I can't tell what the weight of your system is, but Zalmans chassi+cooling+PSU weights in at 22kg.
With only traditional air cooling you can go low cost, low weight and for many systems reach an inaudiable system (over background noise). So as long as you can reach a point where you are satisfied with the cooling and noise level traditional air cooling is unbeatable.