We can all control how we talk, but some seem more conscious of it than others. As someone who (thinks he) can notice a switch in vocal register like any other obvious pattern change, the behaviour also screams out to me each time I see or hear it. But I don't dislike it; the speaker merely has a job to do and a social environment to fit into.

I hear something similar in some (particularly American) men. It's an over-emphasis of the depth of their voice. I think I've noticed a fair few others over the years but there are likely a million other traits in people of all ages that I've never noticed. All designed to influence the listener in some way. After all, people don't typically speak to grandparents the same way they speak to friends. Why not?

It's probably a primal, perhaps evolutionary behavioural trait, but my point is that it's not specific to vapid celebs. We probably all do it to some degree.