Interesting. Probably it shouldn't sound so left-balanced but maybe something else is going on.
I hear (har har) different Mega Drive/Genesis models have different sound qualities, stereo problems too:
http://www.sega-16.com/forum/showthr...-from-bad-ones
http://retrorgb.com/genesisaudiomod.html
Maybe it was recorded with one of the worse models and nobody noticed?
Or perhaps your model is different/clearer?
(if you compared with real hardware; emu music I guess wouldn't replicate the analog-ness of the FM chip and would be a lot clearer)