So The American Heritage Dictionary defines Book as “A set of written or printed pages fastened along one side and encased between protective covers.” Books are physical things. You can touch them, smell them and see them. They are often works of art.
E-Books are digitized information. They are not books. You can only read them through your computer, E-Reader or some other device. Those things aren’t books either.
Sure, one can store hundreds of E-Books on a device, but it looks lousy on a book case.