Wrong. Read the Sheldon page (please!). Long ago there were 700A, 700B, and 700C tires. They were all the same outside diameter, but since the "B" and "C" tires were fatter than the "A" tires, the corresponding rims were smaller. Eventually, "700C" rims were the de-facto standard for "racing" bikes, and tire width changed while the rim diameter stayed constant.