Music used to generate revenue from the radio, from CD sales, and from concert tickets. Changing that business required upsetting several apple carts at once. TV is similarly complex, revenue is derived from advertising, cable carriage or retransmission fees, and direct sales of DVDs. You can’t go digital without first rethinking the entire business (and not every player in the ecosystem takes that lying down). But not publishing. Books are published and sold at retail. In the end, once the only channel from which revenue is derived starts to get remodeled, it’s not long before the whole structure gets torn down and rebuilt to accommodate the new dominant distribution model.