The only thing I can think of, which might explain why Episode 1 looked different, would be that for trailer the saturation was higher. I mean, even some of the OT stuff looks a little more saturated than usual (but still less than the PT). The sabers in Episode 1 were quite subdued on the DVD transfer, but if all they did was increase the saturation for the trailer while still using all old transfer footage, it's possible it has made it seem like there is a new transfer for Episode 1 in the trailer. I did notice some pink in Darth Maul saber fight still, so who knows...

(Yes, I do know there is a new transfer Episode 1 confirmed by the ILM documentary, but it's possible it wasn't used here still.)

I guess the only way we will know is when they start showing clips or specialised trailers for each film for the blu-ray a la 1997 SE release.