I'm going to add another thought...they want you to come so that everyone can see that you are okay w/the relationship/marriage.
Another thought is that they aren't really going to send you an invitation, but by asking for your address, they knew it would get back to you and wanted a reaction. If that was the case, it's a passive move on their part. By not reacting, you aren't giving them the satisfaction of getting angry or upset.
