Expensive sushi restaurants they grate the wasabi root at the table. The standard joints, green dyed horseradish. But they do get it very fine! It's like a play-doh texture.
Horseradish is a fun to grow perennial and can be invasive. We had some in the garden when we bought our place and it is fun to dig up and grate fresh.
I forget what the compounds are that make horseradish pungent, but they dissipate very quickly in the air, which makes the horseradish not pungent any more.
It is pretty much impossible to find real wasabi in the supermarkets. Most wasabi pastes are horseradish. I've found 100% real wasabi powder on Amazon for a reasonable price and it can be re-hydrated and served like the yellow mustard that's served with BBQ pork and sesame seeds.