My husband's nephew had a very quiet family wedding recently, absolutely not bothered we weren't invited, it was just immediate family from both sides. My husband sent a card with a cheque for £100, which we would have thought might have warranted some sort of acknowledgement, it wasn't banked until ages afterwards, but absolutely no thanks via a text, phone call, e mail or thank you card. I hasten to add that he, the nephew, and his wife are both lovely, but my husband, I think would have appreciated some sort of thank you. However, it won't spoil the relationship, I guess "thank yous" are something the older generation were brought up with.