I think there's probably a group that likes having physical copies for the enhanced accessibility and the ability to do whatever you want with the book afterward. I know I would prefer to purchase a physical copy, because I know that the physical copy is completely under my control, and I can resell it, give it away, borrow it to a friend, etc. without a vendor's permission. I expect many publishers are trying to promote eBooks because they can charge the same without any shipping or manufacturing costs and because they can track and control users much more tightly, preventing used sales and compiling profiles about users' tastes, etc.