At one gathering, everyone, except one couple, belonged to a group (let's say, people from Class of XYZ, for example.) When it came to making a welcome speech, the person who had to speak would not mention the couple's names. "They don't belong to our group," he said in an annoyed voice, "And they've invited themselves. So I am not going to welcome them." The couple, who had actually come because they had heard so much about the fun gatherings of the group, never came again.
A friend of ours had invited us to his son's wedding, at X city. I wrote and accepted. He later sent an email, saying that the wedding venue had been shifted to Y town, about 200km from X city. I accepted again, especially because Y town was a place I'd wanted to visit for a long time. He emailed me back, saying, "No, we cannot have you at Y city, it's only for family members and close friends." Try as I did not to take this in bad part, I did feel quite offended, because it was obvious we hadn't fallen into either of the categories he mentioned... and we did not attend either the wedding, or the reception held later in X city.
In both these cases, I feel that the exclusion only made for bad feelings, and should have been handled very differently.
In the first case...I strongly believe that the very fact of welcoming someone is a tacit statement that they are NOT part of the group; the point is made without ever raising it. When I say, "welcome to our home", I am definitely making it obvious that my guest is not, usually, part of my home. So, by saying something like, "Welcome to the gathering of XYZ group, we hope you'll come regularly," the person could have made the couple welcome and yet conveyed the message that they were not part of the group. The couple might not have come again, but they would have done that without feeling bad.
In the second case....when I have invited someone, who has then accepted, and I change the venue later, and email someone informing them about it...and they accept, I think I should gracefully invite them. I cannot imagine that for a grand wedding (which is what this one was), the presence of two more people can make any major difference. Or, at least, I would email them and say, "You are most welcome, but (eg) accommodation in Y town is rather a problem, and we have to set aside half of the rooms for the party of the bride/groom, so it would be great if you could join us for the reception later." Saying it this way, instead of saying, "Sorry, you can't come to the wedding at Y town", is surely a much better way of doing things.
Feelings are very important, and sometimes people need to recognize the fact that other people are important, too. I strongly believe that including people is better than excluding them, for any reason at all...often, the included people don't accept the invitation, but they feel good about being included..and that's what matters.