the thing about evil dead is that every movie was a movie of its own. the serie didnt really carry the same story, just the same character experiencing new events.
scream was just a lame serie in my mind. the scream serie seemed --to me-- that they made the story up as they went along (although they CLAIM that the idea for the movies were thought up as a trilogy)
the best way i could explain it is relating the idea with LOTR. three seprate movies that continue from the last til the final showdown (or whatever it might be)!