The PS3 shots *are* embarassingly bad but it's likely that Monolith, like many other developers who aren't Sony or 1st party Sony studios (Insomniac, etc.) focused on the X360 version first and then reduced the quality of the models and textures to fit them on the PS3.
More importantly though, shame on Sega's marketing department for releasing such terribly uninteresting and downright bland screenshots for the game. Maarten is being kind by calling them "mediocre." They're much worse than mediocre.