It should have ALL the holidays that are observed in the calendar of the United States. If you’re in the U.K., I don’t think you’d see Independence Day or Thanksgiving on your calendar, right? Other countries also have specific holidays they observe that may differ from ours. But there ARE holidays that are pretty universal such as Easter and Christmas - though Christmas is observed on differing dates depending on the country. We also have New Years Day, M.L. King Day, Presidents’ Day, Daylight Savings Day, etc. that other countries don’t.
Whether or not someone “observes” certain dates or not, it’s still a good idea to at least show them on the calendar for informational purposes.
Yes, I agree, for all the major religions.