Well the word "sushi" actually means the kind of rice they use. It isn't exactly fair to call it a catch since that's the dish. And at the all-you-can-eat sushi chains in California I've been to, it is always against the rules to remove the rice. In fact that seems like a common rule at all asian buffets I go to.

If they start making the fish super-thin that's quite lame though. A buffet chain near me did that as they were trying, unsuccessfully, to survive. I also once went to a regular sushi places that had an all-you-can-eat special and who kept ("oopsie") accidentally bringing way more california rolls than I ordered.