Q: message 'for iOS only'

I am selling an ePub on iBook Store. When people are ready to download the book from the store on iBooks for OSX (laptop and desktop), they get the message 'for iOS only'. There is no problem reading it on OSX, but this message is confusing for readers. How can I bypass or sidestep this message? Does every download on iBooks OSX give this message? See images.