I think a physical book has an implied message: this is real, this is permanent, this is important. The mere fact that they take up so much space on my daughter’s bookshelf indicates their importance. Digital media are, by their very nature, impermanent and ephemeral. That too contains an implied message.
My daughter is 9 years old and like everyone of her generation (in industrialized countries, anyway), she is growing up surrounded by digital media. I don’t want her thinking that books are similar to video games or websites. The medium itself contains an ideology.
In addition to that, some folks think that books are inherently beautiful. There is an artistry and a permanence to the medium that can’t be replicated through a digital substitute. I’m especially thinking of things like children’s books, art books, coffee-table books–any book where the aesthetic appeal is not only from the text itself but from illustrations, artwork, layout and design.