The programs used by Warner might be below par, since these are new movies where digital processes should have easily make the picture shine even on DVD. Superman Returns, 300, and HP5 are all Warners, nobody complaining about Transformers, Casino Royale, or other other studio releases.
Maybe casanegro speculation have a point, they want to make the difference between HD and DVD more discernible to common eyes, and thus justify HD higher prices...