I'm not entirely sure why you think this is snobbery any more than describing any correct cooking techniques. This passage is factually correct (apart from the wasabi - with a caveat). Sushi is usually accompanied with delicate fish and the sushi chef has to assume some things about how the person will eat it. Obviously, you can eat your sushi any way you want just like you can cook an omelette any way you want. But if you want to know what a typical french omelette tastes like in France, you need to know how to prepare it. That the last step in preparation for sushi is left up to the eater does not change anything in my mind.

So if you are interested and are willing to set the snobbery issue aside, I will tell you what I know. The reason that shoyu is not added to the fish before it is served is because the salt can ruin the texture of the fish. Actually a surprising amount of fish is pre-salted. When you go to a good sushi restaurant, very frequently the chef will tell you to try something without shoyu first. Some of it is obvious (like shimesaba), but there are times when the chef has decided that the fish needs some pre-treatment which includes salt. In that case you probably don't need any extra salt and he will tell you.

Many people don't realise it, but sushi is actually the name of the vinegared rice. Anything with this vinegared rice is sushi. You can have it in a bowl and it is then called sushi meshi. There are many wonderful sushi donburis as well. While it is tempting to think of the value of sushi as being the sashimi perched on top, good sushi is all about the rice. Especially nigiri sushi (where they form in in the hand and place something on top), the way it is formed is crucial to the taste and texture.

That being said, it's quite important when eating good sushi not to soak the rice in shoyu. Of course it is up to you what you do, but I don't think it is unusual to have a feeling that good sushi is being ruined any more than having a very high quality steak and completely covering it in catsup (so you can no longer taste the steak you ordered).

When you apply the shoyu, the normal technique is to invert the sushi so that the sashimi is pointing mostly down and then to dip the edge into the shoyu. This gives you enough salt to complement the flavour of the fish without overpowering it. It also leaves the sushi (which the chef has spent a lifetime perfecting) intact so that you can take advantage of its quality.

Wasabi is a tricky subject. In a very high quality sushi shop the chef will put the correct amount of wasabi between the sushi and the fish. He will watch you eat it and will be able to tell if he has judged the amount correctly. He will adjust accordingly. In a high quality shop, there will be no wasabi offered to be put in your shoyu (in my experience).

This is different from eating sashimi. With sashimi (without the sushi), you get a plate of fish that is accompanied with condiments. The condiments can be wasabi, ginger, sliced green oinion, types of seaweed, etc. You put what you like in the shoyu and dip the sashimi into the shoyu. My wife criticises me for making the wrong choices for what I put in my shoyu, but I live with it ;-)

If you go to a lower class sushi shop (where they are just shovelling out the sushi), very frequently there will be no wasabi between the sushi and the fish. This is because they have no way to tell how much you will like. In this case it is common to put wasabi in your shoyu. If you go to a very bad sushi place which is essentially using machines to put the sushi together, it's often a good practice to take the fish off, put wasabi in the sushi, dip the fish in shoyu and put it back on the sushi. This is because it is crappily put together in the first place so you might as well take some care in reassembling it.

If you go to a very, very bad sushi restaurant, they will often put a lot of wasabi (really hoseradish and mustard) between the sushi and the fish. This is because the fish is off and they are trying to mask the flavour. I don't think it is worth going to these places.

Hope this helps in understanding (my understanding of) the reasons for sushi eating guidelines. I hope it doesn't too snobby (except for the recommendation not to eat at places that serve spoiled fish).