in my case i would say its a mix of both the person(me) and the technique of my partner(hes very good at stimulating me! ) so i guess it just comes down to luck in the end 69her in a way, because not all women as u said have sensitive nipples and or the partner to take his time trying to pleasure her this way, all i can say is your wifes very lucky- because i know what shes been through!!