I suppose that since the beginning of time, women have always preferred to skip to the loo together. And good friends have no problem with stall-to-stall communication. After all, we can share 'stuff', giggle about our dates and fix each other's outfits.
Do you suppose that men would feel more free to answer nature's call and chat if they used stalls? Or do you think that men are different creatures who prefer to get in and out without any shop talk?!