I think it is possible that Lucasfilm's technicians would be so short-sighted that they used an old NTSC master for the US DVD release and an old PAL master for European/PAL DVD releases.
Because PAL has higher vertical resolution, it could make sense to make anamorphic NTSC discs from the PAL sources, for those who have equipment that don't handle PAL.
I live in Europe, and over here most equipment supports NTSC too. I don't know about the US.
(yeah, I know PAL/NTSC is technically more about composite signal than resolution... but anyway)

Also, when doing upscaling in software, advanced upscaling and post-processing algorithms could be used that are much better than those used by any TV or DVD player.