So what makes a book, exactly? Physically, it's a bunch of words that are laced together in between covers, right? Do comics not follow this format? We'll answer for you—yes they do. Ergo, comics are books. Not to mention, with Kindles and the like out there, the form in which traditional books have come in has morphed in tune with more digitized times, yet they're still considered books, right? Also comics are also referred to as "graphic novels"—of course they should clearly be categorized as actual books!
Besides, comics aren't all super folk in latex suits and capes. Much like the aforementioned graphic novel (again—novel), "Watchmen," comics can create gripping narratives that express deeper themes far better than any Kurt Vonnegut book can. So kindly dismount from your high horses, loosen up, and read a comic, okay?
We're all about breaking boundaries and everything, but there are some things that just are the way they are, period. When you think "book," you think of a lovely, bound text which may contain a few illustrations, but which is dominated purely by the printed word. This is how it is, and this is how it forever shall be. Ergo, comics are not actually books.
If we start to include something like a comic into the whole "book" category, where do we stop? Is a magazine a book then? A pamphlet? Certainly not! Don't even get us started on the "hot dogs are sandwiches" or the "cereal is soup" debates...