I haven't had really any graduations to attend yet, except for my nephews (and of course they'd get a gift). But I was invited to a wedding a couple of years ago for a second cousin. Gave a gift (a very well-thought-out gift, if I may say, with a story/history behind it, which I also relayed to the bridal couple). This was in early June. In late September, I got a thank you. It was a preprinted photo of the couple that said, "Thank you for sharing our day with us." That was it. No mention of the gift and nothing handwritten.
I thought that perhaps they somehow didn't get the gift , until my sister said she got the same TY. I came to the conclusion that my gift (or any of the gifts, for that matter) just didn't matter to them enough to actually put forth the time to write a line to thank the giver specifically for the present, nor for the time I spent picking the present out, relating my story/history, etc. And that's fine; if it's not to their taste, so be it. It's too bad that they couldn't see fit to actually thank us for the gift, but that's, I suppose, their right.
But I have to admit that it clouded my view of them when I got invited to a baby shower a year after that. Because no, I then had no interest in putting more effort into gifting them with something (for an obvious gift-giving occasion) when the previous gift was never even acknowledged, let alone have appreciation expressed for it. Thus, the thank you note (or lack thereof) for the previous gift DID affect my view of them. I wish them well, but I'm not going to put forth any more time or money to gift them for anything again.