zombie84 said:

Pagz: In late 2003, Lucasfilm did an HD telecine of the films, which they colour-corrected, added new effects to and had cleaned by Lowry. The 2004 DVD set was a standard-def downconversion of that. The HD version was always intended to eventually become the highest-quality master (i.e. for blu ray), but it seems they did attempt to fix a couple issues people complained about by taking that master and tweaking it ever so slightly.

Someone mentioned before--these are the masters being used for the 3D conversion. I wonder therefore if the extra brightness boost is not actually an attempt to fix anything but merely compensating for the dulling quality of the polarized 3D glasses. Michael Bay did this already with TF3--he boosted the brightness of the master so that when audiences saw it in 3D it would have the same luminance as a regular 2D print. I mean, even TPM is way brighter, slightly unnaturally so in some shots, and it never had any of the dullness and black crushing issues of the OT.

re: the fixes

This makes me wonder if they'll bother to do a fresh scan for the 3D conversion in 2015-17. I mean, if they're inserting fixes like the wampa arm into the 1080p scan from 2004, then maybe Mr. Ward really wasn't kidding when he called this a "digital negative that we can use for theatrical if we choose to do so." Granted, they already did this in 2004 with the new Jabba model, but still....

re: your second paragraph

Zombie, perhaps you're overthinking things a bit? They did a new 2K scan of TPM, and that was probably for two reasons. 1) It needed a new scan anyway since the old transfer looks pretty terrible by today's standards and 2) They needed a nice cinema-resolution scan for the 3D conversion.

But I don't see why any 3D-related tweaks such as brightness boosting would be on the blu-ray transfer since, well, this is 2D.