First, Pepita, I am so sorry for what you and your son are going through.
As for the original post, I've been there too- I made a quilt for a girl with leukemia and gave it to someone to give to her. She and her mother post regularly on the Caring Bridge website (for people in the hospital to give updates) but I've never seen a word or heard anything about the quilt. It bothered me at first but when I realized this girl is literally fighting for her life it didn't seem like such a big deal.
We would all like acknowledgments, that's true. And we don't do this just for someone to rave and gush and all that. Heck, it embarrasses me when I get a normal thank-you, much less something like that. So I would say you're not being heartless, just a human with a heart, and a good one at that.