> Perhaps a good example is portable (and other) music players: good ones let one quickly go through the content by artist, album, genre, name, etc. as well as custom playlists. Where are they on disk? Doesn't matter.
Really bad example. I'm still searching for a music player that allows me to select music by filesystem location. Any ("consumer device" as you say) I can find shows you your music by artist or album or genre, and it doesn't pose me a problem (I won't use it though) as long as I can select files and whole directories from a filesystem.
Because I know where the music is on the filesystem even where I don't know the tags (because i'm the one who put the files where they are).
Even when I find one program that allow (a limited and degraded) filesystem based selection, it never allows to choose a directory and "play recursively".
Every music program will show me a pile of all the music files it can find on my device with some tags whose content is foreign to me (because I didn't tag them myself).
Actually, it's the same for ebook readers. they insist on either having each their own book directory (separate from the other app, so you won't share resources) or show you a "drawer" with all the books it can find. I'm happy to bypass this bookshelf view each time I can.
By the way, the very first program I _must_ install each time is a two panel file manager.
And tag systems relies on the existence of a complete and maintained tag database and tagged object database.