They are all public domain books in the USA
There are many books that are in the public domain in the USA that are not in the public domain in other countries (and vice-versa).
I suspect this is why the option is hidden for non-US installations.
Originally Posted by Tom Swift
I am still amazed that this fact is never mentioned whenever this service is brought up. These are all public domain books and they are blocked and I have yet to find any mention of this policy on Google or Sony. When I first did a search about this issue, the first thing that appeared was my initial post! Crazy.