OP, it sounds to me like the cash bar for all beverages was the cherry on the cupcake of frustration for you and your husband that day. It's awful that the groom actively recruited him to be in the wedding party and then set about to treat him shabbily. I don't blame you for not giving the gift, nor for leaving right after dinner, and if I were in your shoes, I would be cutting these people out of my life.
I agree with previous posters that timing and content count, as far as any rudeness involving the Facebook post.
As for cash bars, I have never come across this issue, not for alcohol and definitely not for soft drinks. Even the sweetest, simplest little church hall weddings I attended down south, for high school friends, etc., always included sweet tea, lemonade, and coffee, at a minimum. However, as long as I knew in advance, I don't think a cash bar for alcoholic drinks would bother me much, (maybe the fact that I don't drink much colors my opinion), but including water only is really low-down and cheap hosting.