It should also be noted that sometimes the original book is out of copyright but not a specific translation of that book. This is true for some of the texts used in the Harvard Classics series. Thankfully, all of the translations used there are in the public domain.
Likewise, even if a book is completely out of copyright but is electronically published by a company, they still have the rights to that presentation of the book and it cannot be posted to MobileRead without the permission of the company. We could of course go to Project Gutenberg (as an example), get the same text, convert it to a form for upload at MobileRead, and then upload it to MobileRead without permission from the company that published the other version of the public domain text.