Spymaster
Plastic Paddy
are they? it's weird if that's all they sell
A bit, but it seems more like different varieties of the same thing which isn't odd and is what most pizza and sushi gaffs do.
There's a small chain of restaurants in London and Paris called Le Relais De Venise who really do serve only one dish. They just do sirloin steak with frites and even the way it's cooked is limited to rare or medium rare.
If you're only going to have one thing on the menu you need to do it extraordinarily well, and they do. Best steaks in London and Paris.