I got to thinking just a little more about something.. The arcade versions of the Konami games had significantly more powerful sound capabilities. I may have been hasty in thinking the compositions were for systems like the NES or X68000. It doesn't make them any less great but my image of such bleak tone in the music is perhaps colored by the fact that these are interpolations of songs put on a platform that can basically play 1 lead note, 1 note for harmony/chord tones and 1 note for bass.

So maybe the NES has more to do with the image of the music than I previously thought.