My family have never expected thank you letters, if I open it in front of them I say thank you then, if not, a text or a phone call. I think some people in my family would actually be offended if I felt I had to write them a note.
DH's family definitely expect letters. Tbf it's not just me that has to write them, he does and the kids do too.
The people we are writing to all have internet access, we talk to them regularly by phone, but for some reason, we have to write thank you notes. DH says it's just custom and they'd be offended if we didn't.
AIBU to think that in this day and age, it doesn't matter how you say thank you, as long as you do?