I have this theory that there are many fewer possible stereotypes than their are groups of people and thus any particular stereotype you should be able to find several different groups which have that stereotypes (by the infamous "Pidgeon Hold Principle").

As a case in point, I've also heard the same sort of stereotype we're discussing in terms of East/West as a gender difference (where it is probably even less true), with women playing the part of the West coast (more important to be friendly and maintain the sense that everyone is polite to everyone, while not bringing tensions out into the open) and men playing the part of the East coast (you tend to know if guys are on the same side or not, and guys are less likely to want to maintain politeness if someone isn't doing what you need).

Again, I'm not at all claiming this stereotype is true, only that I'm always amused by how many different groups (or contrasts of groups) any given stereotype must apply to.