What Would Emily Post Say?

Recently I was invited to a friend's wedding. The invitation was addressed to Hubby and me. However, H., who has lived with his girlfriend for several years now, was invited to the same wedding sans guest. I found this deeply disturbing. Clearly the line was drawn at "marriage" being the status that would require paying for two guests vs. just one at this particular wedding; but is that really what is the correct thing to do? What about same-sex couples? Should it be ok that their respective partners be excluded from social functions such as weddings merely because they "only live together"? While I wholeheartedly respect the institution of marriage, I also respect those who choose to not enter into it, and those who legally cannot. I can't help but think that by excluding "life partners" but including spouses is the bride's way of imposing her social mores on her guests in that she will exclude whom she wants. Obviously, as the bride, she is within her right to do that; but should we, as a society condone this type of couple-ostracism? Am I looking too much into this? I would love to hear what other people think about this topic!