That's true; it's definitely not as dynamically extreme as a lot of modern mixes. The peak volume reaches really high at times but the average level is not absurdly low; you can set it at a decent level to hear the dialogue without having to turn down the action scenes. If you have it cranked up to the point of being completely deafened by the action, then chances are people's voices are bordering on uncomfortably loud as well.
Part of this is because neither analogue Dolby SR encoding nor any of the present day digital formats yet existed, and so mixers at that time were not in the habit of using routinely and purposely using such enormous contrasts. Even in SW's 70mm mix, which has a far broader and more satisfying dynamic range than any other version of the movie, a certain degree of general restraint is applied for the sake of the total balance. There are some really powerful room-filling rear channel effects at times, such as the sound of Ben's lightsabre in the cantina scene and his earlier krayt dragon call, and often the high frequency response of spaceship engines can be very strong (although I do wonder if mixing for the X-curve in cinemas may have influenced this, since the highs decay much more in a large room than they do in a small home environment, but the EQ of the mix was largely unchanged for the 1993 laserdiscs). But the concept of proper dynamic range is not simply a measure of how extreme the loudest and quietest moments are--it's also about how you use all the intermediate volume levels and what is appropriate where. This is something they did exceptionally well back then, but like so many things it's easy to get it wrong.
I can't actually test the lossless versions, because I don't have them available. I mixed in just three channels using the stereo tracks and the LFE, and then sent these to Satanika to be turned into 5.1 format. He did upload the six-track wavs to usenet, but I haven't tried to download them since my access to it hasn't been good and I can't play multichannel PCM on my current equipment. I'd be surprised if they actually sounded any different from the AC3 aside from the increased fidelity, but I can't say for sure myself.
Off-topic, but I'm still all verklempt after seeing the last Harry Potter movie. Wow . . .