God knows. I suspect the publishers are still wedded to the idea of Hardback - Pricy, Paperback - Cheaper. Given the e-format is the same for both it just seems like profiteering; the same way DVDs retail at £13.99 on release then a few months later are down to less than half that. Or that Blu-Ray which has a production cost similar to DVD retails for ~50% more. It was the same with CDs and Cassettes/Vinyl - back then the argument was they deserved a premium price as they were better and the public expected better products to be more expensive.