Humans are unique. Each one is unique in his/her own regard. Like your thumbprint, your life is unlike any life in existence.
Celebrating your day of birth does not rob God of his rightful glory. Quite the opposite as it glorifies the life of a single unique individual in the scheme of all time, a testament to it's designer!
The fact that humans even feel the want to celebrate life separates us from all other known life! That "want" was put into us from our creator.
And if you don't believe in a creator it is still a testament to a intricate and beautiful process of how this unique life came to be.
I know forgoing birthdays doesn't seem like a large request of an organization... but it's the principle! JWs gross misconception of birthdays is but the tip of a large iceberg of absurdities and contradictions.
-Sab