ok, my take on the way news anchors talk…
on the general way they talk:
the microphones have a limited pick up area and frequency range. they can also magnify lisps and other irregular speech patterns. instead of being able to understand the news anchor, you could just get a bunch of bursts of static because the man or woman is a heavy breather when they talk. most of the anchors are trained to talk a specific way for clairity sake - for coast to coast understanding and to have a clear sound.
on switching to a story or live report or such:
they have to make sure that the camera men, reports, and other TV people are prepared to make the transition. changing the way they speak it to get everyone’s attention. that way there isn’t any dead air or reports caught picking their nose on camera.