I’m pretty sure the following generalization is true, with few exceptions: every iPad app has been designed for a preferred orientation. I think this is true whether the designer was conscious of the preference or not.
I’m not saying that the non-preferred orientations are poorly designed, nor am I saying that they’re not useful. I mean only that every iPad app has an orientation in which it looks and works best – the way we say of a person’s appearance that he or she has “a good side.”
Here are some examples, off the top of my head:
- iOS 7 lock screen (see above)
- Photos (especially shared Photo Streams)