I tried to file this in the same category as https://bugs.freedesktop.org/show_bug.cgi?id=97107 , but bugzilla wouldn't let me !
Incidentally, that bug# is related. It seems application/x-sega-cd-rom and application/x-sega-pico-rom are the only ones to have a <glob pattern="*.bin"/>, so every unrelated .bin file - magic or no - gets identified as Sega ROMs. I'm willing to bet > 99% of .bin files in the universe are not Sega ROMs. Well at least in mine.
Would it be possible to add a generic "application/x-bin" type , or "application/x-raw-dump" (or any other appropriate name) that can be the default fallback for .bin extensions ?