Many of the rituals and doctrine of the Church, particularly in the concentrated form of the Vatican, are so distant from contemporary American mores that it's kind of hard to see why this would be a big deal. But it seems to be. I'm no expert on liturgy or doctrine. But this seems to have been more than a departure from tradition. It actually seems to be a violation of the prescribed liturgy of the Church.
This liturgical requirement seems to have fallen to the wayside in many US dioceses. But it's been a point of controversy even recently. In 2005, the Archbishop of Boston washed the feet of women but did so seemingly over the objections of the Vatican. He consulted with Rome and the Vatican "affirmed the liturgical requirement that only the feet of men be washed at the Holy Thursday ritual" but said it was his decision as Archbishop.