Yeah I was invited to be a groomsguy once. Seemed kind of odd, although I would have obliged. It's irrelevant because I couldn't attend the wedding anyway as I was already going to one on the same day.
Doesn't really seem like a big deal to me. Wedding parties are a relatively new invention in the first place. For most of history in the US you would just go to a courthouse with a couple of witnesses and boom you're married, go home and eat some cake with the family and that was all there was to it.
