In this case, 'not exactly the same' is just semantics. Sure, there are a couple changes in sound effects, a missing music cue added back, some reversed stuff is now unswapped, and the third rear channel is discrete instead of matrixed; but these things don't really amount to much in the way of actual significance. Like zombie said, the entire sound and 'feel' of the mix is vastly different than anything that was made in 1977, and even though the Bluray corrects some of the most egregious technical oversights, this is comparable (if you'll forgive the overdramatic example) to putting a bandaid on a major stab wound. To have a version that sounds right, the only choices are either to do it over again, maintaining similarity to the original in all aspects; or better yet to simply use the real thing and be done with it.

In the course of my audio studies, it has become increasingly clear to me that changes in sound have to be made carefully and with great attention to detail, because the only way to undo them is to go back to the source and start over. Things like equalization and dynamic range compression are impossible to reverse once they've been applied, because they fundamentally alter the tonal qualities of the recording. My professors have emphatically emphasized on many occasions that it is far better to get the sources right from the start and have good quality material to work with, rather than using messed up tracks and trying to 'fix it in the mix' afterwards. The official SW mix has some of the worst-sounding EQ that I've ever heard—together with the screwed up balance between elements, it has the effect of emphasizing distorted and boxy sounds to the exclusion of all else. Even the most talented audio engineer in the world would have a tough time salvaging it into anything remotely listenable.

Fortunately, the original mixes have all been archived at extremely high quality, so the only thing stopping them from being heard is the resistance from those in charge.