In an interview with The Guardian, when he was 83, Sendak said:
Ebooks: “I hate them. It’s like making believe there’s another kind of sex. There isn’t another kind of sex. There isn’t another kind of book! A book is a book is a book.”
More interesting stuff in the article.
See also this article in The New York Times Arts Beat which has some more good Sendak stuff, including links to an interview with Stephen Colbert.