I don't think the author's premise of defining America's different subcultures by geographic region alone is terribly sound. The are many important cultural divides. For example, based on population density, i.e. urban versus rural. Two people living in major cities of different states may have more in common than a urban dweller versus a rural person within the same state.
Other relevant cultural divides are based on ethnicity, social class, age, and religion.
Take a look at the right/left dichotomy that is really a culture war disguised as political partisanship. It's old versus young, rural versus urban, white versus non-white, religious versus secular, and south versus northeast/west. All of these distinctions undergird the cultural divide. Not just region. It's why every state has red and blue districts.