Since weekends (and holidays) are included as normal days in the sprint, for multi-week sprints this assumes that you have 2/7 more days available in the sprint than is actually the case. On the sprint burndown chart this leads to almost a 30% understatement of the required burndown rate (slope) to finish the sprint on time.

An option to ignore weekends and a custom holiday calendar would be the ideal solution. I don't think it would be worth adding automatic support for international calendars based on location because each team might work to custom calendar (for example if they are supporting a product in a different locale). Also, going in once a year to add the 10-20 public holidays for that year seems like a very acceptable overhead for a flexible solution.