Not directly related to the trailers article (which was good: congrats, Gf), just addressing a tangent that came up:
There is actually a rule about this, for studio/union pictures anyway. adam yax mentioned it, but is a little off on the details.
Here’s the scoop: You can do the opening titles essentially one of two ways. You can show the studio and the name of the movie, and nothing else; or you can do the full opening-credit lineup, as negotiated by the various artists. The first style is relative uncommon, but an example would be Pirates of the Caribbean. Examples of the second style abound.
So you couldn’t say “20th Century Fox presents / A James Cameron Film / TITANIC” and then not continue with actors, writer(s), producer(s), composer, editor, and so on. Ditto, you couldn’t say, “United Artists presents / Daniel Craig as James Bond in / DOCTOR NO,” and then proceed with the film without further titles. If you name one person, you gotta name 'em all, at least, again, as has been negotiated for opening-title status.
The Star Wars / Lucasfilm issue was in the interpretation of the Lucasfilm credit. The practice of “title only” was not common, but it wasn’t unheard of, and Lucas argued that since “Lucasfilm” was the company and not the individual it should be acceptable. At the time, Lucasfilm wasn’t much of a production company, and the credit was interpreted by some as a sneaky way of saying “a film by George Lucas.” That, under the rule described above, was a no-no, unless the credits continued with “starring Mark Hamill / Harrison Ford / etc / music by / costumes by” and so on. However, nobody expected the movie to make much of a splash, so the complaints were mild, and didn’t prevent the movie from coming out as Lucas had intended. Then, when Empire Strikes Back came out, the same sequence was used, except this time the WGA objected. Lucas appealed to the DGA, but they didn’t back him up; this may be due to the fact that Irvin Kershner, not Lucas, was the director of the second film, and the DGA didn’t much appreciate the way the “Lucasfilm” credit implied that Lucas was the director. Lucas paid some hefty fines and resigned from the guild.
(I did all of this from memory, so I might have some of the specifics slightly wrong. In particular, I don’t remember exactly the sequence of complaints on Empire, whether the WGA objected alone and the DGA joined them, or vice versa, or what. Other than that, though, I’m confident that it’s pretty close.)