Its about the same
Well, here in the Tokyo airport I had a chance to find out. I ordered a few things to get a sampling: Fatty Tuna, Salmon, and Yellow Tail. It was excellent for sure - The fish was fresh and the rice was soft and sticky. The ginger was smooth and the wasabi was, well, it was wasabi.
Overall, this experience was comparable to a high quality US Sushi bar. (Safeway need not apply)