Yes because he clearly knew they would be such a success at the time he was negotiating contracts. He made the standard contracts, which is what you have to do, because you can't just change the terms later based on how successful something is or isn't.
This isn't a case of Lucas being exceptionally greedy. Maybe its a case proving how 1-sided Hollywood contracts are, though.
While I agree with you, the article is about Return of the Jedi which was released in 1983 - six years after the first Star Wars movie came out.
So by the time these contracts were being negotiated with David Prowse, the producers of the project knew that the movie was likely to be highly successful.
This isn't a case of Lucas being exceptionally greedy. Maybe its a case proving how 1-sided Hollywood contracts are, though.