What people are addicted to, is a menu they know at a familiar place. Starbucks wins because it's familiar, not because it's any better; it's the brand, not the coffee.

Also, coffee and tea are drinks that people will accept even if they aren't exactly a person's preferred style/flavor.

People will order and drink coffee at any restaurant when the choice is generic coffee vs. decaf. Brand certainly helps but many people, even picky, will drink a brown liquid called coffee anywhere, if the primary objective is conversation, reading, etc.