If you play a lot of highly compressed MP3s or use a crappy sound source like an iPod then the M60s might be just a tiny bit more forgiving of compressed or poorly recorded music. Not a lot more forgiving though, the M60s are still extremely accurate and bring out the worst in the worst recorded music. More importantly though, they bring out the best in the nicely recorded music or movies.
However, for just about anything else, movies or music, M80s seem to have a slight edge. Of course that is what the M80 folk keep trying to convince us M60 owners anyways. <snicker>
With great power comes Awesome irresponsibility.