When I lived in London I used to visit Westminster Cathedral regularly. One afternoon I heard Gregorian chant coming over the speakers. It was not piped music but actual live singing of the Divine Office. A friend of mine who knows these things remarked that (a) all Cathedrals are supposed to have public recitation of the Divine Office and (b) Westminster is pretty much the only Cathedral in the world that does. When in Rome I have attended Vespers at the Basilica of the the Holy Cross in Jerusalem* and again at the Basilica of the Floating Ceiling. In the former case it might only have been happening because I turned up on the Feast of the Triumph of the Holy Cross. The point is that my friend is pretty much right.
*(Despite the name this church is in Rome.)
Anyway the New Liturgical Movement blog has an essay on the subject.
I have said this several times in the past, but most American cathedrals are essentially overgrown parish churches, and this paradigm has so ensconced itself in our liturgical consciousness that many bishops see their cathedrals as model parish churches for their diocese.
It's one of those rules nobody keeps.
(I am pretty sure New Liturgical Movement can be translated by something better than Novus Liturgicus Motus).