That actually goes for investors in general, from what I can tell. Biggest mistake we made with the first investor that invited us in was assuming that he knew what we did. (One of his associates apparently had said that he should talk to us; he'd never looked at our website.)

In the case of YC interviews, that paragraph that says what your company does is buried in the thousands of pages of text that are going across their eyes during the screening process. Don't expect them to remember it verbatim. ;-)