I’ll throw this one out to the film geeks here. Sometime in the ‘60’s (I believe) the bulk of the credits for American films, originally run at the start, were relegated to the end of the film. About the same time, it seems, credits were extended to include nearly everyone who had a job on the production (just once I’d like to be a Best Boy or Clapper Loader). My questions are: 1) did this change happen on a fixed date, and 2) was this mandated by an organization such as the the MPAA, was it a gentlemans’ agreement among the production companies, or something else?
I think we did this before. The answer is complex.
Films as far back as the silent days had end credits. Usually the major credits were at the beginning, with a review of the cast at the end (the idea of that was so you could put the actor with the role if you’ve actually seen the movie – though some old films showed pictures of the actors in the opening credits).
As far as this was concerned, there was no fixed date; a few films started doing it, and once the major credits appeared at the end, it was a simple matter to add more names – people didn’t have to sit through them and get impatient for the movie to start.
The big hurdle was the Director’s Guild. They required that the director’s name be displayed immediately before the film began. This was broken with “Star Wars: The Empire Strikes Back,” where Irving Kirsner’s name didn’t appear until the first credit after the end of the film. George Lucas was fined for this, which he paid out of the first hour’s receipts. 
Since then, the guild changed its rules to allow a later placement, but still a prominent one. This usually means the director’s credit is the first after the film ends.
It is up to the individual director to agree to putting his name at the end. Nowadays, main credits sometimes appear at the start of the film and sometimes at the end, depending on how they want to do it and if they can get the director to agree.
Speaking of credits check out the DVD Audio Commentary for Bring It On, the guy does a whole thing about the credits - v. funny 