The toughest of questions can be answered with the simplest ideas.
There seems to be some issues regarding the sand. Quite simple in fact. Everyones sand is dirty at some point or at least most of the time. To answer how the Japanese picture sand is so "clean" is like this..
If the sand is dirty, you sprinkle a thin layer of fresh white new sand along the surface just enought to cover the old. This does not seem like a bad idea at all because, the layer is not that thick, and it gives a "fresh" - "clean" look. Thats how they avoid snails and other cleaners. But that leaves the edges, how are the edges cleaned?
Simple, depending on the type of algae along the edges, there are two - one that is on the substrate itself and the other on the glass between the substrate. You have 2 methods here. One, use a scrapper to go down below just enough so that its gone, and or - take a thin piece of plastic, slide it between the glass and the sand and push it towards the back. At that point, a "crevice" is made to deposit another thin layer of "fresh" - "clean" looking sand. The plastic is removed and this is continued throughout the tank.
Of course you would do the sides before you do the top
That is my theory. After a while there is probably a buildup. They would more than likely move out a certain amount of substrate not to affect its biological ability and put in a new layer of substrate and repeat the process.
This theory would avoid any creatures needed to keep the "sand" clean.
JMO
Kris
I agree with Steveweast. 
