I bet it heavily depends on the source (ie: animation / live action, length, etc) for making mpeg2 look good. Even though the trend is that BR mpeg2 has been looking better, that's not always the case. Some recent mpeg2 reviews have not been as positive (Haunted Mansion comes to mind as a recent not-so-good mpeg2 release).
Honestly, tho... who cares about the codec as long as the movie looks good!
It is totally incorrect to say that mpeg4/vc-1 are better then mpeg2 IF bitrate is not considered. These newer codecs allow better picture at a lower bitrate, but do not in and of themselves produce a better picture. Actually the best picture is either totally uncompressed or one of the lostless codecs. The problem mentioned with some of BD discs is that given the uncompressed audio used not enought bit rate was given to the MPEG2 to produce a really quality HD picture.
All of that is changing with the latest discs, most of which are in VC1 or MPEG4.