Originally Posted by cybmole
all books published prior to 1924 are free everywhere, not just at amazon
No, that's not entirely true.
Although anything published prior to 1923 is in the US public domain, that doesn't automatically mean that it will be free. There's no prohibition on charging for public domain works.
It certainly doesn't apply "everywhere". Many books which are in the US public domain are NOT in the public domain elsewhere. An example is Agatha Christie's first works; "The Mysterious Affair at Styles", for example, is in the US public domain, but not in most other countries.