I can't answer your question but I don't think sushi is just fish over rice.

I just came back from Tokyo where I visited several highly regarded sushi restaurants. Rice and especially the temperature for which it's served is highly important. I ate a chirashi bowl and while the fish on top was excellent, I was actually more impressed with the rice. I also like how there's that perfect balance. The chef makes a piece of nigiri and you put it in your mouth. No need for extra soy sauce or wasabi. The fish melts in your mouth. On one day, I went to an excellent restaurant for sushi at lunch and didn't have plans for dinner so I stopped into a kaiten (conveyer belt) sushi place. I left after eating 2 plates (4 pieces). I had eaten at this kaizen place before and enjoyed it but after having a great experience for lunch, I just couldn't do it.