I find it weird that so many people on this thread expect to be an A list friend to everyone, and if they're not, they're offended too be 'only an acquaintance'.
I'm very happy to be invited to the evening do of someone I get on well and I'm friendly with. I'm not remotely offended that I'm not A list or family, but they'd still like me to be part of their celebration. Being offended strikes me as really odd.
If it's a long way away and expensive to go to, then don't go. But they're no need to be snarky about it or offended. Or as one person said, to withdraw from the friendship.
I got married in the days when there was only one reception and it meant leaving out people I liked. My daughters wedding wasn't at all flashy and they were on a tight budget, but as she's very gregarious, there were more people that she wanted to share her wedding with, then they could afford to have a three course meal for.
Fortunately her friends at work and her old school friends etc, didn't have any qualms at all about accepting an evening invitation, and it was a really lovely and happy occasion with everyone letting their hair down.
It strikes me that those on this thread who are mortally offended at being B list, wouldn't be adding to the joy at all, so no loss to the bride and groom.