I believe there are different types of music listeners:
a. Purist - a listener who sticks to one or two genre's, or even sub-genre's of music. They may find it easier or perhaps don't have the time, money or facilities (friends with big music collections, extensive record shops, the internet) to listen to music of all varieties. Other factors may come into the equation - close mindedness, the fashion appeal / cool factor of the music etc.
b. Music lover - loves all music, within a selection of genre's, which conform to their personal tastes. Such a listener may have no interest in sub-genre's, as they enjoy the experience of exploring it all.
c. Music fanatic - loves music from a huge variety of genre's. May find listening to different genre's allows common grounds to be met with other "purists". May enjoy the process of manipulating moods through the crossing of genre's (smooth jazz for dinner, dub n reggae for lazy weekend mornings, psy for partying after dinner). Such listeners may find that to please their healthy appetite, they may need to prioritise and limit which genre's and sub-genre's they search for music.
d. Mp3 wh0re - wants everything and anything, most likely in a specific genre only.
e. Occasional music listener - enjoys music but doesn't know the difference between psychedelic trance and uplifting trance. Has no need for genre's, usually content with "good" or "bad".
And probabbly some more I have forgotten
To conclude, some of us (most mentionably purists and music fanatics) need sub-genre's to help us out. Whereas others can happily live with just a good or bad indication.
I believe that a reviewer shouldn't be forced into supplying a sub-genre style if they don't feel confident in doing so. Past reviews have shown that someone else usually comes along further down the line to provide one.
I'll be taking this all into account in the music review tool I am developing. Any further input is much appreciated