If the family for whom you made dinner is experiencing difficult circumstances (like, say, you made dinner for a family whose child is in the hospital, or who has received tragic news), then I would excuse them for not writing a thank you note.
If you hand delivered birthday gifts to a family, and if they opened the gifts while you were there, and thanked you, I'd be inclined to consider that enough. If they opened the gifts later, I'd expect a note of gratitude in reply.
My FIL no longer sends birthday checks to one of my husband's sister's kids because they never wrote a thank you note. He has mentioned several times that he always appreciated getting a note from my kids, and they still get a small check on their birthdays.
I think it's best not to expect anything when you want to share something with someone. Make sure you're giving the gift without any strings attached, and be generous. But also, make sure to teach your kids to say thank you, and to learn how to write a proper note. That's where you can make the difference, and somewhere down the road, someone will appreciate your family's ability to express gratitude.