I'm not sure what the rationale is for which screens in the app can be flipped between portrait and landscape, but the restriction on portrait-only in 2.20 and later is because in previous versions, when Recommended was flipped to landscape, the image width was increased to the phone's landscape width, but the image height and aspect ratio was kept the same. That meant that the top and bottom of the image was cropped in landscape, but not in portrait (which may be what you meant in the last para).
The fix to that problem was to restrict Recommended to portrait. It's perhaps not what I might have done, but I don't know anything about the internals, so there may have been compelling reasons to do it that way.
"Help and About" can also be portrait and landscape.
There also seem to be some issues with Recommended image aspect ratios in the current app (2.26) compared to the image aspect ratios in the "What's On" emails. A good example is the Recommended image for Sound Of Music, where the image is stretched a bit horizontally compared to the image for the same movie in "What's On" (where the aspect ratio looks OK). There seemed to be some other aspect ratio differences between the app and this weekend's "What's On", but they seemed less obvious than for Sound Of Music.
