I think Gaiman's right in terms of someone who borrows a book from a friend or from the library (which is partly why I'm saddened by Harper Collin's recent decision on libary ebooks) because people who borrow a book from a friend, or get it from a library, are respecting the copyright of the author. Sure, they're reading for free, but not illegally. I would NEVER download an illegal book, but I happily patronize my library (ebook and paper) and then Gaiman's right: I am more likely to buy a future book by an author because of something I read for free.

People who are willing to steal books will probably continue to steal, rather than buy.