I've designed two epubs of my novel. One coded specifically for Nook and one specifically coded for iPad (this one required a lot of specialized html coding to get around bugs and errors specific to iBooks). I'm trying to explain to someone that they are not interchangeable, that the special coding I did to get photos to be centered in iBooks won't look the same if you view the same epub file on a Nook device. That sort of thing. Neither of us own an iPad or Nook, so it's hard to tell.
Can someone verify this for me or prove me wrong?