for the main holidays (easter, thanksgiving, and christmas) we have stuff like turkey and ham. sometimes at christmas we'll have a huge italian meal with lasagna and meatballs and stuff since we just had a huge turkey meal a month before.
for stuff like mother's day and father's day and summer/early fall birthdays, we'll usually have bbqs. my birthday dinner is usually thanksgiving (i know, what a rip off).
this year both my parents are busy all day sunday so they're going to pick up the fried seafood from a local restaurant and make some easy stuff to go with it.
maybe they were just having lobster at christmas as a fun thing for you? i've never known anyone to do that around here.
oh, and nick and i eat mussels like once a week. they're probably the grossest looking food ever but they are wicked good.