You missed the point, Boost. It isn't a charity thing on Lucas' part, it is a contractual (and therefore legal) obligation which he is getting out of by claiming that Return of the Jedi (one of the most sucessful films of all time) has yet to turn a profit. Just because other studios do it does not make it right.
It is also no secret that George has a thing against Prowse, so, as Mielr already asked, is Prowse the only one being told this, or are all actors getting the same treatment.