presents for development

Why do we celebrate birthdays? One answer might be to give toys that are appropriate for the age of a child. Games to practice some skill that corresponds with the developmental age of the child. For my first child, I used to read the age on the label and I was often disappointed because the toys didn't interest her. Now I'm more into books and stuff that is appropriate for different ages and children. I can look at a child and observe and see what it does, why and what it needs. Rarely does the anniversary correspond to a transition to another stage of development. Or am I wrong?