The modern nigiri sushi we know was invented as fast food for busy travelers in 18th Century Tokyo (known then as Edo). Bite-sized grabs of rice and raw fish were treated with kelp, vinegar, light soy sauce, herbs and other zests to stall spoilage and make the goods last longer.
Now, with refrigeration so widely available, seasoning each piece of sushi has become a luxury treatment rather than a preservation necessity. As a result, that kind of classic Edomae sushi — especially made with fresh Tokyo Bay catch — will burn a hole in your wallet the size of Idaho. But hey, no harm in gawking at pictures, right?