Want to own a book? Buy a hard copy. Amazon, Apple, Google, B&N eBooks are only licensed.
From a paper written by Nathan Savage Libraries, eBooks & Copyright Law we read:
In addition to not owning Amazon’s “digital content,” those who license the content from Amazon will be limited to viewing it “solely on the [Kindle] device or as authorized by Amazon as part of the service,” which is to say that content from Amazon will only be viewable on a Kindle, or in one of the Amazon-created applications made for computers, cell phones, etc.
Barnes & Noble, Sony and Google have similar restrictions explained in the article. Digital rights management software does a good job in protecting the rights of the publishers, unfortunately user rights have somehow a lower priority.