It's important for food retailing companies to incorporate local preference. It's not only starbucks but also some food retailers that have each menu in each area. For example, Ohsho, a famous Chinese restaurant chain in Japan has carried out the policy "We provide foods suitable for each area"
But, when it comes to standardization of menu to simplify tasks of the employees, it's not consistent with that policy.
I guess the best answer is "foods served in one metropolitan cities must be standardized, because there will be relocation of the employees between each restaurant. But, menus can differ between different metropolitan cities, because there won't be relocation of them and they can approach local food preference to miximize sales."