I agree she is definitely more pop over rock but I think the hall of fame isn't exclusively for rock and roll artists now. To me it seems like it's more of a collection of popular and influential musicians since rock and roll isn't the dominant form of popular music. Afrika Bambaataa is most definitely not rock and roll but he was part of the people who revolutionized DJ culture in hip hop.
P.S. Did you know The Beastie Boys opened for Madonna during The Virgin Tour?
