Now famous is the story of David Prowse, the actor who played Darth Vader, and how he cut a seemingly lucrative deal for residuals on Return of the Jedi. Despite the fact that the film has grossed so much money it could pay for the entire nation of Russia to spend two weeks in rehab, Prowse is repeatedly told he is owed no residuals because the film hasn't turned a profit.
How does that happen? It's called Hollywood accounting, and it's more evil than the Sith Lord, himself. Basically, in order to keep from paying portions of net profit, major movie studios will do their accounting in such a way as to minimize the money a film appears to make.
Here's an example: Big Name Studio wants to make a film called Action Man 2, which will undoubtedly be a blockbuster. Big Name Studio creates a separate company called "Action Man 2, Inc." Action Man 2, Inc. needs studio space, equipment, overhead, etc. Well, Big Name Studio is happy to provide all of those things, for the low price of 2 billion dollars. Action Man 2, Inc, and by extention the film Action Man 2, is already billions of dollars in the hole. Nobody involved in the production is actually in the hole, as Big Name Studio effectively paid the billions of dollars to themselves. Again, the whole point is to avoid paying their fair share of residuals (and, in many cases, taxes)...and David Prowse ends up getting the shaft.