To me, a middle aged white guy, Vonzelle and Nadia are very similar both musically and in appearance. Two tall black women singing soul music (or at least in that genre). Bo and Constantine are both long haired rockers and the two blonde babes were similar in many ways.
My theory is that if you like a particular genre, you will tend to vote for somebody who signs that style. For instance, if you think Stevie Wonder is Gods gift to music, you have to vote for Anwar.
What soul music did Nadia sing? I must have missed it. I remember Paul McCartney, Cyndi Lauper, and another classic rock song she did, but I don't recall any soul music.