The author does mention this possibility in one of the final paragraphs, that maybe every actor in the film /except/ Julia Roberts and Bruce Willis look differe

The author does mention this possibility in one of the final paragraphs, that maybe every actor in the film /except/ Julia Roberts and Bruce Willis look different in the Ocean's 12 universe - it seems to be what the film wants the audience to think, and though it's a bit silly, so are the films :)