1) They are long lasting. It takes on the order of, say, ten or fifteen hours to read a book during which whole time your loved one is thinking in the back of her head how much you must love her for getting her such a lovely gift. Then, after she's finished, it will sit on her shelf in her living room or her bedroom and remind her of you.
2) They are personal, intimate even. When you get your loved one a book he really loves, he not only enjoys the book, he feels full of warm, fuzzy feelings that you picked it for him, that you knew him so well you knew how much he'd like it, that you think so highly of him you matched him up with this really great book.
3) Don't know how to pick the book that will result in #2 above? Books have a solution to that problem too. Walk into, say, the Gap and describe your loved one's personality and interests to the people working there, and they will not be able to pick out a sweater well suited to your loved one. Walk into a bookstore and do the same, and the people there absolutely will. Today, as part of Small Business Saturday, authors will be visiting local independent bookstores across the country to help you pick the perfect book for your loved one. (Find one near you with this handymap and/or google your favorite bookstore to see what they have going on today.) They aren't selling their own books, you understand; they are going to meet you, listen to you talk about your loved one, and offer the perfect book. (Authors tend to be very well and widely read, and this is our superpower. We are like Santa in this way.) That way you get to say to your loved one not only have I given you this great book but it was picked out personally for you by [insert name of fabulous author here].
4) Even if -- perhaps, especially if -- your loved one owns some kind of e-reader, a book still makes the perfect gift. Now it's retro and nostalgic (sort of like the holidays themselves, especially for those of you still eating Chex Mix)(which should be everyone because Chex Mix is awesome). Now books stand out. Now your loved one will say, fondly, "Oh, I remember reading real books. How lovely." Personally, I like to go back and forth -- one ebook, one paper, one e, one paper. Your loved one will love having an actual object to unwrap and hold and smell and flip through and examine the cover of and then, finally, read and reread and look at and remember.
5) As regular readers will recall, books make great Christmas trees. Here's ours from last year. You can't do this with an ebook, my friends.