^^ I think publishers are just assuming everyone's gonna strip DRM and put it up on P2P networks and charges them accordingly
Seriously though, a paper book takes up space, whether in a bookstore or warehouse while thousands of ebooks can be stored in a regular HD- so there's more incentive for merchants to sell the paper books if only to free up space for new stock. I doubt if this is the main reason why they price them like that but I think it's a factor.