Well I'd rather they told me the night before than not at all - I mean, if they're not ready to get married, then they're not ready to get married. It's important that commitment is taken seriously.
And realistically, if they'd announced it 2 weeks beforehand, most people wouldn't be able to get refunds on their travel plans anyway. So I'm in two minds as to whether there was any point telling earlier. If they knew 3 months beforehand? Definitely rude. But not all weddings go ahead as planned. People were committed to their travel plans to attend the wedding, so it didn't make a huge difference at that point, although I'm sure it was disappointing.