That same thing happened to my husband and I before we were married. His best friend (since they were 13) got engaged after we did. His friend had called to ask him to be in the wedding, and both he and his now wife know me fairly well. Well, the save the date card came a few days later and was only addressed to my husband, not even 'and guest'. So he called them to ask if I was invited cause if not he wasn't going to be in their wedding (he didn't mention that to them) and his friend said yeah, blamed the girl (and really it was her fault as she wrote and mailed them) and put her on the phone. She said it was a typo and other people complained too. Fine. That was that.
Then the invitation comes to the rehersal dinner, no mention of my name. So again, he calls to ask, this time to see if the dinner is literally wedding party only or if i'm invited (we live in DC and the wedding was in Baton Rouge). They said "yeah, of course, we just made a mistake on the envelope". Normally we wouldn't have even asked that, and I would have just skipped it, but since we were going to be out of town, and staying with my in-laws in New Orleans, which is an hour away, I couldn't just come or go as I pleased. Then an invitation comes to some party their threw themselves and says 'Joey and guest". They too had our invitation by then and knew my name, etc. So I was a little insulted, but it was better than not being on there at all. Then the wedding invitation comes and also says guest. If these were strangers it would be one thing, but my husband was in their wedding, the groom was in our wedding, and the bride and I knew each other so there was no excuse for not writing my name.
The best part was that she got mad at all the grooms friends (my husband included, even though we live out of state and only saw her at the rehersal, dinner, and wedding) and 'demoted' them from groomsmen to ushers at the wedding. They weren't even allowed in the church during the marriage! They had to wait outside to open the doors for everyone at the end! So compared to that, my name not being on the invitation seemed small.
Oh, another thing I find odd is that I'm in a friend's wedding in April and she just told me that she told one of the bridesmaids that her boyfriend can't come to the wedding. Is that a normal thing? I know if I had told her that at my wedding she would have been very annoyed, so I'm not sure why she's doing this at hers. Guess I'm glad I'm married as she can't really not invite my husband!