My lovely friend-since-school is getting married. We are in our early 40s and thought it would never happen for her, so we are all thrilled on her behalf.
She announced to a bunch of us that she was not going to invite us to the wedding because weddings are, like, expensive and, you know, difficult to organise, so it's just easier if no friends go. 
She might think about doing a picnic celebration where everyone brings their own food and drink sometime after the wedding.
She didn't register the
looks on our faces. She has been to all of our weddings, eaten the food, drunk the -shedload of booze, danced to the bands etc.
So as not to drip feed, she also has form for wangling herself invites to weddings of acquaintances (she is a bit of a social butterfly) and critiquing the food, speeches, venues, etc. She has been a guest at dozens and dozens of weddings.
So AIBU? Should I just nod and smile and think how lovely that she is doing it her own way, even if that doesn't involve long term friends?
Or ISBU? Wanting a small wedding I understand. But isn't rude for her to tell friends that they won't be invited to the wedding, despite her being a guest at their celebrations? And to do it all without so much as blinking.