Not sure if this or the Comparison list were best for this.
In the actual comparison: http://www.dvdcompare.net/comparisons/film.php?fid=2232 there is a note that says "Poor image quality – too many episodes on one disk, resulting in compression artefacts".
My problem with this note, is not so much that it is true, but rather that it (and the conclusion) can be interpreted as that the R1 has better image quality, which is not the case. It is just that it isn't the result of compression artifacts, but rather:
1. It is a PAL->NTSC conversion (expected, since the show is a mixture of film and video).
2. The colors are much more washed out.
3. It is generally softer (more so than can just be explained by the PAL->NTSC conversion, can see this in still frames).
4. The film elements has more wear-and-tear-issues.
I have the whole 8-disc UK complete boxset, and disc 4 from the US boxset, and can create some image comparisons if anyone wants it.