I have 16 nieces and nephews. I stopped giving them presents when they got old enough to dial a phone to say thank you....not because of their age, but because I figured that if, by the age of 12, they didn't know how to say thank you to someone for a gift, they didn't want any more gifts! I have one niece that still gets a small gift from us.
These children all now have children of their own. I have sent gifts to their kids, and not once received a thank you in return, from the kids or the parents, except from one niece (the niece mentioned above). Her kids are the only ones that get gifts from me now. (They are little, like not quite 2 and 4. she will call me, and hand them the phone to say thank you to auntie.) Might make me a bad person to some, but I expect my kids to say thank you no matter what, and it bothers me that they even attempt to say thank you (parents or kids). Guess I have higher expectations for my nieces and nephews than their parents do...
My kids have never gotten gifts from my family, or DH's. Wait...once, when she was born, DD#1 got a baby blanket that my oldest sister crocheted, and once her husband brought DD#2 and DS a present when he was in town for work. Other than that, my kids never got anything, not even a card. With both my girls expecting their first babies, neither one expects anything for that as well. The niece above has sent DD#2 some bby items she received, but never used (boy related things) and bought her a couple of things off her registry. DD#1 is just newly pregnant, hasn't really announced it, but that niece has some things to send her as well, and told me to let her know when her registry is up.
ETA: My husband knows the pain of birthday/Christmas gifts. His birthday is a few days before Christmas, and he would get the same amount of gifts as his 2 siblings, but be told that a couple of them were for his birthday (and wrapped in Christmas paper). His brother would get school clothes for his birthday (August). His sister was the only one who got decent gifts (March)...unless it was Easter, and then her presents were partly from the Easter bunny.