Dave, I also liked this explanation you gave, and definitely agree with the truth of Category 3 (based on my observations), although often it seems to me that teens may be fixated on a certain genre since they are young and just haven't had as much time to explore others. Plus, they are in a "learn myself/express myself/find myself" through music stage, I think.
I'd probably classify myself as a meraber of Category 4 since I don't listen to the radio, except when captive at work, and I don't really listen to any one genre. Plus, I think your explanation of Category 4 fits me perfectly, heh heh!
Cute story, nonsubmissivewife, and a valid observation!