Thank-You Notes

I am a Canadian who lives near the U.S. Border and a lot of people from both sides often meet and get married. A couple of years ago, a Canadian friend of my husband got married to an girl from Michigan. The wedding was held here in Canada and the couple are residing in Michigan, as they work there etc. For their wedding I gave them a gift which I had their wedding date and names engraved on. It turns out that this "wedding" was not even a real wedding as this was their "spiritual ceremony."..whatever this is , and that they would be legally marrying in the future due to legal and immigration issues,. I found this odd , then I still did not receive a thank -- you note . Then, after their child was born, I gave them a gift as well as a gift for her other daughter she had with a boyfriend five years earlier, so that the older girl would still be remembered. It is now almost two years later and I still have not received a thank-you letter for any of the gifts, nor even a verbal thank-you for the gifts. In Canada it is considered to be a very rude and ignorant to not send a written thank-you note for a wedding gift or other gifts received at a milestone event or celebration in one`s life. Apparently, other guests did not receive thank-you notes either. Is this a general practice and acceptable in the U.S. Culture? If so, then I guess I would understand, but here it would be a huge faux pas to not send a hand written thank-you note as well as an obvious lack of any class or basic manners to omit this duty. Can anyone assist me in this inquiry ?