Very simple.
Lots of American foodies believe that "authentic" = "superior." This applies exclusively to what are marked as "ethnic" cuisines: French and Italian high cuisine places can do "Asian influence" and be called innovative, but people who don't look like white Europeans only have good food if it is served in exactly the centuries-old form that has been selected by some know-nothing reviewer who's happened to catch foodie attention. This same crew generally puts Japanese food at the top of the pyramid, for a number of reasons, and is ignorant and stupid enough to believe that the top of the Japanese food pyramid is sushi. They are also ignorant and stupid enough to believe in the "centuries-old culinary tradition of sushi" and all that nonsense, as if it were not quite clearly documented that what we generally think of as sushi (as opposed to the preserved, pressed stuff) was invented in Tokyo in the late 19th century.
So put together the pieces:
These restaurants are the pinnacle of authenticity. You can tell, because you can only eat this sushi the "right" way, as determined by a chef who is, after all, Japanese. Variation in taste is denied; such things are not authentic.
The fact that all of this is complete garbage, insofar as a Japanese restaurant in Japan is concerned, means nothing: since when has being a rich foodie yapping required that you know anything about the topic at hand?. In Japan, at sushi places and high-end places (they usually aren't the same thing, folks), it is usual to provide various sauces for dipping and such in a fashion that encourages diners to make their own choices. The chef may very well say "here's some ponzu, but you're not going to need very much -- take it easy," but he's making a friendly suggestion. You want lots of ponzu, you go right ahead.
These chefs probably do serve very good fish, well prepared, on well-made rice. But they can get away with charging a fortune because there are a lot of idiots who think that if they pay a lot and are treated imperiously by someone with a funny accent the food must be superior. The fact is, they can't actually tell the difference with their mouths, so they have to be told. And one way to say "this is really good sushi" is antics like these.
As to things like spicy mayonnaise fake crab rolls, well, yes, that is pretty nasty. But it's certainly available here in Japan, the primary difference being that people who buy these things buy them at the supermarket or the cheap lunch place; they know very well that this stuff is junk food. And you know, if you're running a sushi restaurant, you don't have to accept off-menu orders, any more than you do at any other restaurant. If you don't put stuff like that on your menu, you don't have to serve it: if someone asks, you can say, "I'm sorry, I don't keep mayonnaise, and I don't really know how to make that roll. Can I recommend such-and-such?" There's no reason to be rude.
The thing I would keep most firmly in mind about this nonsense is that restaurant service in Japan is generally exceedingly polite and gracious. If your restaurant really serves authentic Japanese food, your service shouldn't be discourteous. If, on the other hand, you can get people to pay more if you are rude to them, good for you: go ahead, fleece them for their stupidity.  | 
