I should have mentioned WHY that Middle Eastern practice makes sense. They're singing songs in scales which differ from each other in subtle microtonal ways - it's easy enough to perceive the basic identity of the scale, but tradition says that the third of one might be a Pythagorean comma different from that in another. So it makes sense for a singer to stay on the same scale for an extended period, so they can get the tuning right. Usually these sequences begin with an instrumental prelude that gets the scale even more firmly locked into the singer's head.

I would bet that the same happens to some extent in Western tradition too. It certainly did for liturgical chant; the whole idea of "mode" was probably elaborated to stop church choirs coming unstuck while doing awkward changes. In the Syrian church, each week in the calendar has its own mode.