Starbucks may deserve all the stick that they get for their labor practices, but here in Canada on holidays they pay double time and a half (or about CAD $50/hour).
Are they staying open because there's marketing value in being open on a holiday, or because there's business as usual money to be made. If it's not for some extra marketing purposes, this just lays bare how much more money they could be paying folks and still remain profitable.
Overtime and holiday pay was meant to disincentivize manufacturing companies from overworking their people and not letting them spend time doing frivolous things like being with family on holidays. The difference between the cost of labor and the value of labor was so small back then (after decades of negotiating, union action, and bloodshed) that a simple 1.5x was enough to disincentivize it under most circumstances. It's so vast now for the service industry that they are willing to pay 2.5 times as much.