I note in my own speech that the normal pronunciation of the au in taught is like that of caught, the broad a of pot, father, rather than the open o of lost or paucity. However, when I speak formally, I tend to pronounce the au of taught only as the lattter, i.e. the open o.
So somehow in my little brain, that open o pronunciation is associated with elevated speech, probably from listening to Roosevelt when I was very little. What I mean is is that in a lot of American dialects, the open o is the norm and I possibly heard people in the newsreels and in the movies speak that way at a time when actors aimed for a New England rather than Midwestern pronunciation.
This is just an example of how we adjust our speech unconsciously (well, conscious now) to various registers, incl pronunciation. Any observations from the rest of you?