Weird, I've never considered them remotely the same.
Buffet: go choose from a very large assortment of offerings and eat all you want.
Family Style: Endless amounts of the same group of food
Again, I like both.
Family Style: Whispering Canyon and Liberty Tree are two we love and go to nearly every trip. Ohana is another
Buffet: Boma, Biergarten, Cape May, Tusker House, Hollywood and Vine, etc. etc.
Buffet is generally a little more loud and bustling. Family Style is a more subdued and quiet. Outside of Whispering Canyon of course.