I absolutely respect your right not to spend any money for birthday gifts or to celebrate the birthday. I understand why and the feelings behind it and support you.
We did something different though. Knowing the gift would be soft or unappreciated, we got an 'experience' as a bday gift: sports tickets we went to as a family, or Circ du soleil or something like that.
Not that I'm saying you should have done that. NOT AT ALL. I respect what you did and know it was harder than what we did. And probably more effective. I was just offering an alternative to doing nothing.