General comment: I think my son must be an exception, because at age 22 he still sends out handwritten TY notes as soon as he gets a gift. I taught him that, but it was his decision to keep doing it.
Anyway, the generic TY note. Considering that a lot of people don't say TY in any form (in person, on Facebook, in writing), I'd be somewhat grateful to get any acknowledgement. That doesn't mean that a bit of effort wouldn't be appreciated. Several years ago we gave a card/money to a neighbor kid for HS graduation. We got back an 8.5x11 sheet of paper with fill-in blanks. All he had to do was fill in what the gift was and sign. This was a kid who was in advanced courses, and quite intelligent. I know, that doesn't mean anything. It was just a bit surprising. To be honest, though, I'd have been more satisfied with a verbal TY.
Is it a hill to die on? No, but the lack of any TY, in any form, is disappointing.