It's all about how they're farmed. Japanese take health and sanitation of chickens very seriously and they constantly do tests. Much more often than you'd see at US farms. US farmers depend on anti-bacterial washings of eggs and antibiotics in chicken feed as the primary defense against salmonella and other bacteria.

Since dishes made with raw eggs are so popular in Japan, they take all these precautions to the max. When I travel to Japan, I have zero worries when I crack a raw egg on top of my ramen, for example. Also, their omelettes are a lot runnier and taste different. I would never do that with US eggs. Also, their yolks are also much more orange/red in color. US eggs are mainly yellow in color.

You can read more here: http://jlec-pr.jp/egg