Why do the Brits have the day off for the royal wedding?

Why do the Brits have the day off for the royal wedding? What are you celebrating exactly, and why does it entail a bank holiday? Why are you so overjoyed over the union of people most of you do not even know? Don't you have DVR? If the wedding is supposed to boost tourism, aren't the tourists already on holiday? (Not that I'd mind a day off myself here in the States?)