They have never remembered mine in the four years I've been with DH (we've only been married 7 months) but it totally pisses me off since my parents have never once forgotten DH's and to be quite honest I'm not even sure they know or care when my birthday is
I wouldn't be angry at all. I am not very good at remembering people's birthdays and everyone that is close to me knows that I don't love them any less if I don't call for their birthday, they just know that I am forgetful!