The article is missing one major reason why people go to Starbucks: the environment and amenities.
From what I've read, it sounds like in America, people go to Starbucks because they actually like the coffee there, but from my observations in other countries (including China), the bigger appeal often comprises the other things that come along with the food and beverage. Clean, temperature-controlled environment, comfy couches, free wi-fi - a package deal that isn't always easily available in all parts of the world. People like to go there to hang out with friends. Or they might go alone with a book or a laptop. They tend to stay there for a while, so while the coffee is not cheap, there is some additional relaxation or entertainment value that they're gaining out of it. Not saying that it's frugal, just pointing out the culture there is different, and the scenario of the office worker who grabs a takeaway Starbucks coffee everyday is probably more prevalent in America, while in China it's possibly more often used as a place to chill out, which may be why some people would rather go to Starbucks instead of getting a cheaper/better coffee somewhere else.