I'd never heard about this either. Those images have been resized, making it more difficult to tell. However, the source is most definitely not the same:

If anyone can upload some screencaps off the ntsc Jedi (mine are just from an LD rip), we can have a closer look at the detail. It doesn't seem counterintuitive to me that they used a different master tape for Jedi - it seems counterintuitive to me that they used what was probably a D-3 tape in 2006 to master a DVD instead of scanning the few Non-SE scenes required to convert the 2004 DVD to the theatrical version. Heck, maybe they couldn't find the 1993 "definitive Collection" master tape for Jedi and just used a different one.

But I didn't know that they released an English THX version in PAL, I'm under the impression that they only released PAL THX LD's in foreign language versions?