Hero in a half shell said:
True Story:
It was originally supposed to be the Wookies that the squad met, not the Ewoks, so the finale of ROTJ would have been an epic battle between hundreds of Wookies and Stormtroopers.
Lucas changed it because Ewoks were more marketable to children, and would sell better as merchandise. He also forfeited his fees in ROTJ and instead took 100% control of the merchandising, it's an incredibly smart business move, but his reliance on merchandise has been to the detriment of his films.
Very close, but you're wrong on one point: it was actually the first
Star Wars that Lucas made sure he had exclusive merchandising rights to, and he didn't forfeit all of his other rights, he just requested that one in his contract knowing he'd get it, because movie merchandising really was not a big industry in the late 70's. He went on to make enough money on toys to personally fund the other five films, not to mention to buy back all the rights to
A New Hope that he did give up (notably ownership of the film itself) back in '77.
Also, I think you're right about the real reason he changed the Wookiees to Ewoks, but Lucas has always maintained that it was because he wanted to do a story about a primitive people helping to defeat a high technology people, and we knew from Chewbacca that the Wookiees weren't exactly primitive. And to be fair to Lucas, the idea first showed up in the gigantic treatment he did for
A New Hope, which was like 200 pages long and needed to be cut into three movies (although the final product barely resembled the treatment.) Basically, in that story, the heroes crash land on the Wookiee home planet and teach them how to fly fighter craft, and the final battle is pretty much Wookiees in X-Wings vs. the empire. So in that version, the Wookiees actually /were/ primitive, and the symbolism he claimed he wanted was intact.
Edit: And derp, I posted in a necro thread. Sorry about that.