Originally Posted by murraypaul
Yes, this is true.
One workaround is to store all your books in a central app, such as Goodreader, and Open In to the app you want to use, but it is a workaround, there is no central file storage in iOS.
That has no relevance to reading. If you try to open an epub from Safari, for example, it will offer 'Open in iBooks' and 'Open in...'. The second option will give you a list of all installed apps which have registered epub as a handled file-type. You are not forced to use iBooks.
Furthermore, the Open In defaults to the last thing you selected for that type of file. It learns what you prefer.