IIRC, Roger Ebert hinted at the time that the 35mm prints may have been deliberately struck poorly, with low brightness, density, and saturation, in order to push the thought that digital, which was then poor resolution, was ready as a theatrical format.
The funny thing is I saw amazingly rich looking 35mm prints of AOTC and when I saw it in digital it was uglier and flat and bland (maybe that theater had the digital set up poorly). When I saw TPM digitally it looked good though, really popping at both theaters (one of each projector type).
And the 35mm print of AOTC I see now has reallllly rich colors, super vibrant and saturated and really rich, deep blacks. If you read Lucasfilm stuff they were also bragging about how they had a better process for producing release prints with less film stages.