You have to understand that Lucas is spending quite a bit of money already "restoring" the classic trilogy. It's just to him, it's far more important to make it more the way he wanted it than to preserve how it was originally. To him, he's trying to ensure that Star Wars will last long after he is gone, and last as a truer representation of what he wanted it to be.
For him to go back and restore the versions of the films he felt weren't finished in the first place is counter productive to his own personal artistic goals.
I think part of the reason he didn't release the O-OT on DVD at all is because he probably felt that the laserdisc Master just wouldn't be up to today's standards. I think that's why it was like pulling teeth for Jim Ward to finally convince him to okay the September solution.
If he were to go back and restore a print of the O-OT, and bring it up to today's standards, it would be for the benefit of the people who actually want those cuts, not Lucas. Sure he stands to make money from it, but only if there is enough interest to off set the cost of the restoration in the first place.
That's why I see this September release as a way to show Lucas that the original versions -do- matter to a substantial enough group of people to make the restoration effort finacially self sustaining.
I agree with your assessment of THX. Lucas certainly knows the consumer dynamic like the back of his hand.
For me in the end, I hold myself responsible for any of my purchases. If I choose to be double dipped, then I choose to be double dipped.