Almost every American food—from egg foo yung to empanadas—is covered in the phone book under the generic heading “Restaurants.” Only pizza stands alone. Pizza, a Johnny-come-lately compared with such long-standing national favorites as the hamburger and hot dog, has secured a special place on the American table. Everybody likes pizza. Even those who claim to be immune to its charms must deign to have the occasional slice; a staggering 93 percent of Americans eat pizza at least once a month. According to one study, each man, woman, and child consumes an average of 23 pounds of pie every year. But...