Not true. London has some incredible Japanese restaurant. Check out Roka on Charlotte Street (Fitzrovia), Umu in Mayfair, and Chisou on Princes Street (Hanover Sq.). All three are up there with the best in the world (in my humble opinion).
a new restaurant in union square called 15 EAST has one of the best sushi chefs (masato shimizu from jewel bako) and a contemporary atmosphere. it's owned by the same people who did tocqueville, so the kitchen food has french/new-american twist.