OP, your culture is absolutely irrelevant in this case.
I have been to dozens of weddings as part of a band, as well as normal invitations that happen through life. A sausage in a roll, or a bacon roll, are far more filling than buffets in my experience and a lot more welcome in most cases.
From your attitude, I am not surprised that you only received an invitation to the evening reception. If the hotel is as 'prestigious' as you say, there would have been no problem for them to get you something to eat had you asked. I highly doubt that there were no packets of crisps etc behind the bar. Free bars are not the norm, whatever you may think.
Did the happy couple 'demand' a gift from you? You do realise that you can choose not to give money, but to give a token of your affection/respect? A wedding does not have to 'cost a fortune', but if you chose to buy a new dress/expensive gift etc, that was your choice.
We are going to a family wedding in the US later this year. We have no idea what to expect, but will be smiling and saying 'thank you for having us', offering to help out if need be and just being very, very grateful that they love us enough to want us to be there with them at this special time.
I think you need a change in attitude. Being invited to a wedding, be it the whole day or just the evening, means the b&g want to spend time with you, and have you there with them to celebrate their happiness. It seems that you have been unable to do that, and perhaps you need to give your head a serious wobble, because you are coming across very, very badly indeed.