To expect a thanks for gifts?

[sheldonconk]

In the past month or so there's been 4 birthdays in my family/amongst family friends. Two of my nephews turned 18, one family friend was 22 and the other 20. I sent each of them a gift and some birthday money. Out of the 4 of them 1 has texted me to say "thanks". No acknowledgement at all from the other 3.
I really don't expect a lengthy 2 page handwritten note but I do think that it's incredibly rude not to take a few seconds to acknowledge a gift via text, email or even fbook. I'm considering not bothering next time.
Aibu?

[Pancakeflipper]

Do people really see saying thanks as a chore?

I like saying thank you.

[Marylou2]

YANBU but if they've reached 18 without a basic grasp of good manners they're not going to start now. It begins at 3 with signing their own name on a thankyou written by their parents and continues through the teenage years when they are forced to despite their protestations. By 18 it should be second nature.