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).I would think that if the BD supporters can make mpeg2 look good, then mpeg4 should eventualy be able to look better.
The only reason on would think MPEG2 could look better is they had enough time to learn it on DVDs.
In reality modern codecs are usually much better and VC-1 isn't new either and taxes the hardware less than h.264 - it's far the best codec, I think.