It's apples and oranges. The Simpsons have a thin thread of continuity whereas Family Guy doesn't, and even makes references to it (Peter's comment on Bonnie's being pregnant for several years) and has AFAIK, never intended or implied to have continuity though it still does sometimes.
Peter has gone through a few jobs ranging from the toy factory to a fisherman to his current job at the beer factory. His father has died. Cleveland got divorced, Meg had/has a relationsihp with the Mayor, Stewie's "sperm" brother was born. The girl Stewie fell in love with made a reappearence. I can go on and on but most of the time the continuity is left at the expense of the gags.