Eric Asimov had an article about the trend toward huge slices of fish on sushi. He mentions places that serve 6 or even 6 1/2 inch slabs of fish atop 2 1/2 inch balls of rice. He explains that this is an attempt to "Americanize" sushi and notes that restaurants that follow this trend have been scoring high in Zagat.
What's the attraction? Why would anyone _want_ to try to handle a hotdog-sized slice of fish with chopsticks? After all, three 2-inches slices are the same amount of fish as 1 six-inch slice. If I were served something so gross, I'd send it back and ask the chef to cut it into bite-sized pieces and give me enough rice to go 'round.
I haven't read the article but I was once informed that there are regional differences in Japan in the cuisine. In some regions the fish is supposed to be the same length of the rice. In other regions the fish is supposed to hang over the sides of the rice. I think in the U.S. the latter style has become exaggerated.
The other sneaky thing is price. The big ones can be very expensive. I went to Yama and ordered my usual 6 pieces of sushi (plus miso soup) and got too much food and spent too much money. I should've know when some peices were $3.50 for 1!!