Some things in life are obligatory. Not all of them are nice and ethical. Not all of them make us the bigger person. Sometimes we must do the petty thing, as this is the only way the message we mean to send will be understood.
If, by any chance, we were to be delicate or choose the mature road, some people would never understand that they've wronged us. Of course, we should be wise when choosing when to take the petty road, because not everything is worth creating a scene for, but some things are, and oh boy, we should squeeze all the juice out of them.
I don't really understand wedding code, because nobody around me gets married anymore. I assume this is a pretty dramatic situation, and that's why the OP reacted that way, especially after travelling so much to get to the event. What I do observe is that many stories reflect the economic nature weddings are acquiring. They seem increasingly more related to cash-grabbing than to celebrating union.
Angry brides demanding expensive gifts their guests can't afford is now becoming the norm. But if you're expected to travel 600+ miles and deliver an expensive gift and you're not even included on the list, I don't think that's a fair exchange, and it definitely deserves a petty reaction.
I don't think OP caused much of a scene; I think he was coherent, and after all, gifts and even presence should be optional. If they weren't, it wouldn't be a party but an obligatory fundraising event, and maybe that's what it secretly is, apparently.
Do you think this couple caused way too much of a scene? Or did they do well by leaving the party with their precious envelope?