I think you are correct.  Unless you're buying directly from whoever caught it the smartest thing is to buy it frozen (in theory).  Most of the time the fish is just thawed out from frozen anyway for presentation.  Sushi is "sushi grade" because of how it is frozen.  But people like to live in the illusion that they are buying directly from the fisherman so everything is thawed out and put on ice even though that decreases shelf life.  But at the same time the customer can at least make some judgment on how fresh the fish is with it thawed instead of frozen.  

 

I think the answer is probably it's more appealing to present the fish on ice than with refrigeration or in a freezer.   

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