I think it's difficult within media type too as there are various use cases. I agree that, probably, general videos thumbnails are not useful, e.g. music videos or home videos, where the best that can be done is the default frame-grab from a point somewhere in the video. However, for movies, to be able to browse by a decent-quality DVD cover or movie poster is a big plus, you don't really need a caption. A simple textual file listing for movies is such a wasted opportunity. TV Series fall halfway between the two - you could probably want nice cover art for the series but for episodes it might be better with just text. It might be more useful to treat those as an album, i.e. large cover art at the top for the series with the individual episodes underneath.
I think my original problem was that images and movies could only be displayed as text, regardless of the default setting. Whether that's a bug or not, i.e. whether it was designed-in on purpose, I don't know but it does seem an illogical design decision if it was intended. Things may have changed in the current version of JRemote, I don't know.
Is that the same as you're reporting? I'm confused now as to the difference between "Thumbnails" and "Image List". Which one displays a file listing with a small version of the artwork to the left and text to the right of it (as opposed to a file listing with text only) - a hybrid list if you like - and which one displays large icons in a grid? I think I would very rarely, if at all, want the hybrid view. For audio, once it gets down to file listing level, I'd want a large-ish album cover at the top with a track listing below, which is given to me by the first view option ("text"). For images and movies, I'd want large icons in a grid once it gets to file-level, the third option. For TV Series, I'd want the view as for Audio, with the entire series artwork at the top and individual episodes listed below.
I think the hybrid view would only be useful for mixed playlists or a Playing Now view, where each track could come from a different album.