I just thought I would add my two cents... I typically forget to call my mom on her anniversary, I do call on Mother's day, and I try to remember her birthday, but she doesn't call on my anniversary or birthday for that matter. I think an anniversary is something that's just for you and your honey... Other people need not make a big deal of it, birthdays are different, I ALWAYS get a phone call from each sister on my birthday, none of my brothers EVER call... And I would never expect their wives to do it for them. Don't make a big deal of your son not doing it, it's very rare for them to do it and if you push it, it's going to make you look like the pushy MIL that everyone dreads.
Good luck!