Japan does sushi best

After spending an extended period of time in my home country, Ireland, I can't help but compare the things one country does better than the other. One thing Japan 'wins' for is sushi. 

In Ireland, people often recommend restaurants that 'do really good sushi' to me. But when I go and try it, it's just not the same. Without a doubt, the sushi in Japan is far better than any I've tasted in Ireland. What is it? Fish are fish, and in theory raw fish shouldn't be that different between countries! So is it the way it is stored or prepped or both or something different? 

Just for fun: of the two pictures in this post, A and B, one is from Ireland and one is from Japan, can you guess which is which?